
Class. 



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Book ^^ V 
Copyright ^".^ 



COEVRIGHT DEPOSnV 



COMPOSITION AND HEAT 
TREATMENT OF STEEL 



rrai"w- 



PublisKed by the 



Ne^v/ "Yoirlt. 



^ompariy 



Successors to tKeBookDepartments of tKe 

McGraw Publishing Company Hill Publishing Company 

Publishers of Booka for 
Electrical World The Engineering and Mining Journal 

The Engineering Record Power and The Engineer 

Electric Railway Journal American Machinist 



COMPOSITION AND HEAT 
TREATMENT OF STEEL 



BY 

E. F. LAKE 

STEEL EDITOR OF THE AMERICAN MACHINIST 



McGRAW-HILL BOOK COMPANY 

239 WEST 39TH STREET, NEW YORK 
6 BOUVERIE STREET, LONDON, E.G. 

1910 



Copyright, 1910, hy the McGraw-Hill Book Company 



.L3 



The Plimpton Press Norwood Mass. U.S.A. 






PREFACE 

In preparing the matter that enters into this book no attempt has 
been made to go into details on the subjects of the ores, their melting down 
into iron, or refining the iron in steel making. This part has merely been 
covered in a general way in order to lead up to and give a better under- 
standing of the effect of the elements present in and added to steels of the 
various grades and kinds. 

An attempt has been made to cover all the materials that have been 
used, either commercially or experimentally, for the purpose of making 
better steel and improving the standard brands so they will have greater 
strengths; withstand strains and stresses better; possess a longer wearing 
surface; have a greater electrical resistance, conductivity, or magnetism; 
attain a greater hardness, ductility, resiliency, or malleability; be ca- 
pable of taking larger cuts on other metals or machining them faster; pro- 
duce a metal that can be easier rolled, hammered, pressed, drawn, forged, 
welded, or machined into shape; be non-corrosive, or, in fact, make a 
better metal for any of the many uses to which it is put. The effect these 
materials or elements have had upon the carbon and alloyed steels has been 
told as well as the data at hand would permit, and hints have been in- 
jected, as to what might be expected from many of the elements, in order 
to stimulate further investigations and experiments. Results have been 
obtained in this way in the very recent past that are truly wonderful, 
yet these are liable to sink into insignificance before the discoveries that 
may be made in the near future. 

The different chemical compositions that can be made from the ele- 
ments here Hsted and described are so numerous that it seems hopeless 
to expect that all of them will ever be compounded, and tests made, and 
the results recorded. However, with the many individuals that are 
working along these lines some combinations are bound to be made that 
will prove to be beneficial, and doubtless some steels will be produced that 
will cause as great a revolution as "Mushet" or "Bessemer" steels did in 
their respective lines. A verj^ few of the possible quaternary steels 
have been tried, i.e., alloys made by combining four different elements 
with the ferrite, and therefore many are yet to be investigated in the many 
different percentages in which it is possible to combine them. And this 
does not take into consideration the compositions that are possible with 
six, eight or more elements. 

V 



vi PREFACE 

Following the ingredients of and materials used in steel, comes the 
heat-treatment, as the two have moved along parallel Hnes, in the many 
investigations, experiments, and improvements that have been made, 
and seem to be inseparable. Each change in composition seems to have 
altered the heat-treatment, and each improvement in heat-treatment seem 
to have altered the percentage, that is best to use, of some one or more 
element. Many different methods and various kinds of materials have 
been experimented with and consequently a great deal of useful informa- 
tion has been obtained and many improvements of a radical nature made. 
New methods, new materials, and new apparatus have thus been brought 
into use for the heat-treatment of steel. These have enabled the hardener 
to get more definite, positive, and uniform results, and in this way the metal 
has been improved to a great extent. 

All of the information that could be obtained on this phase of steel 
making and working has therefore been recorded as carefully as possible. 
This also suggests ideas that would indicate that there is still room for 
important improvements or discoveries. One of these is the attaching 
of a positive and negative wire of an electrical circuit to the piece of steel 
to be hardened and place it in a quenching bath. The current can then 
be turned on, the piece heated, the current turned off, and the piece 
quenched without moving it or allowing the air to strike the metal and oxi- 
dize it. Another instance is the possibilities suggested by carbonizing 
steel with gases or chemicals and thus doing away with the old laborious 
method of packing the steel pieces in bone and charcoal. Still another 
is the 30-minute annealing of high speed steel and the possibility of a 
similar method being applied to carbon steel. 

In gathering together the data necessary to add to my own, very little 
credit has been given to individuals, as to make this correct is not only 
a laborious but a hopelessly impossible task. To illustrate this I have 
seen professors claim as their own discoveries, new principles, new methods, 
etc., that were developed and perfected by students in their classes, and 
shop foremen and superintendents claim as theirs, inventions made by 
men in the shop. Two important discoveries that developed into new 
kinds of steel were made through the mistakes of workmen in steel 
mills. Two men on the same job added the correct percentage of a 
material and thus this element was twice as large as it was thought 
would give good results. In fact, it was believed that it would injure 
the metal to add more than a certain percentage, but when this maxi- 
mum percentage was doubled the metal was given properties that were 
very beneficial for certain purposes. None of us can add but a mite to 
the knowledge that we have obtained from others and because we are 
enabled to write it so it will be recorded in books and papers does not 
give us the privilege of claiming to be the originators of certain ideas, 



PREFACE vii 

principles, discoveries, or inventions. Every one who has worked in the 
4teel mill or the laboratory is entitled to a part of the credit for any new 
ideas or information that may happen to be enclosed between the two 
covers of this book. To pick out a few individuals and give less credit 
than this would be working an injustice and stating an untruth, and to 
name all that should be given credit is a physical impossibility. 

E. F. Lake. 



CONTENTS 

CHAPTER PAGE 

I The Making of Pig Iron 1-12 

Ordinary blast furnace reduction of ores, 1-3; Use of excess gas, 4; Con- 
veying molten metal in ladle cars, 5; Making pig beds in sand floor, 6; 
Casting pigs in iron molds, 7-8; Electric blast furnace, 9-12. 

II Bessemer Process of Converting Iron into Steel 13-21 

Burning out impurities, 13; Recarburizing, 14-15; Casting into ingots, 
16; Acid and basic Bessemer process, 17; Metal for ingot molds, 18; Steel 
rails, 19. 

III Open-Hearth Process for Making Steel 22-33 

Stationary and tilting furnaces, 22-27; Charging machine, 28; Acid 
open-hearth furnace, 29; Basic open-hearth furnace, 30-31; Other open- 
hearth processes, 32; Fluid ingot compressor, 33. 

IV Crucible Process of Steel Making 34-41 

Kind of crucibles used, 34; Regenerative furnace, 35; Charging crucibles, 
36; Pouring ingots, 37; Hammering ingots, 38; Making into bars, 39; 
Wrought iron, 40-41. 

V Electric Furnaces for Steel Making 42-63 

Stassano revolving furnace, 42-43; Heroult furnace, 44-47; Keller fur- 
nace, 47-48; Kjellin and Colby furnaces, 49-53; Rochling-Rodenhauser 
furnace, 53-56; Girod furnace, 56-61; Summary, 61-63. 

VI Ingredients of and Materials Used in Steel 64-110 

Carbon, 64-71; Manganese, 71-75; Sihcon, 75-77; Phosphorus, 78-80; 
Sulphur, 80-83; Oxygen, Hydrogen, and Nitrogen, 83-86; Copper, 86-88; 
Arsenic, Antimony, and Bismuth, 88-90; Boron, 91-93; Tantalum, 93; 
Platinum, 94; Nickel, 95-97; Cobalt, 97-98; Chromium, 99-100; Tungsten, 
100-102; Molybdenum, 102-103; Vanadium, 103-105; Titanium, 105-108; 
Aluminum, 109; Tin, 109; Yttrium, 110; Cerium and Lanthanum, 110. 

VII Working Steel into Shape 111-150 

Rolling, 111-115; Rules for rolling, 115; Temperatures, 116; Apparatus for 
melting metal for castings, 116-117; Risers, gates, etc., 117-118; Composi- 
tion of steel castings, 118-119; Vanadium steel castings, 119-120; Titanium, 
120; Nickel-steel castings, 120; Direct-steel castings, 121; Manganese-steel 
castings, 121; Chrome-steel castings, 122; Forgeability of different steels, 
123-124; Effect of temperature on the grain, 124-126; Hand-forging, 126; 
Steam-hammer forging, 127-130; Drop-hammer forging, 131-135; Pressed 
forgings, 135-143; Welding, 143-145; Electric welding, 145-147; Welding 
with gases, 147-149; Thermit welding, 149-150. 

VIII Furnaces and Fuels Used for Heat-Treatment 151-184 

Theory of heat-treatment, 151-152; Hard-fuel furnace, 153; Liquid fuel, 
154-156; Oil burner, 156; Over-fired furnace, 157-159; Under-fired furnace, 

ix 



X CONTENTS 

CHAPTER PAGE 

160-162; Water- jacketed front, 162; Gaseous fuel, 163; Oven furnace, 164; 
Revolving retort and upright furnaces, 165; Automatic furnaces, 166-169; 
Gas-booster, 170; Automatic temperature control for furnaces, 170-173; 
Heating in liquids, 174; Lead-bath furnace, 175-176; Cyanide of potassium 
furnace, 177; Barium-chloride furnace, 178-181; Electric furnaces, 182-184. 

IX Annealing Steel 185-191 

Theory and methods, 185-186; Rules for hammered stock, 187; Laws 
on annealing, 188-189; Apparatus for annealing, 190-191. 

X Hardening Steel 192-213 

Theory, 192; Microscopical examination, 193; Ferrite, 193; Cementite, 
193; Pearhte, 194; Martensite and Hardenite, 195; Sorbite, 195; Austenite, 
195-196; Troostite, 197; Effect of composition and hardening, 197-199; 
Baths for hardening, 199-202; Methods of keeping bath cool, 202-204; 
Electrical hardening, 204-205; Cracking and warping, 205-208; High- 
speed steel, 208-209; Hardening furnaces, 210-213. 

XI Tempering Steel 214-226 

Negative and positive quenching, 214; Temperatures at which to draw 
tools, 215-216; Failures when tempering by color, 216-217; Effect of 
tempering on springs, 218-219; Effect on strength of steel, 220; Mixtures 
of lead and tin for tempering baths, 223; Tempering furnaces and baths, 
220-226. 

XII Carbonizing 227-246 

Different kinds of carbonizing, 227-228; Factors governing carbonizing, 
228-230; Carbonizing materials, 231-232; Results obtained with gases, 
233-234; Speed of penetration, 234-235; Effect of temperature, 236; 
Heat-treatment after carbonizing, 236-237; Time of exposure, 237-238; 
Carbonizing with gas, 238-245; Local hardening, 245-246. 



COMPOSITION AND HEAT-TREATMENT OF STEEL 

CHAPTER I 
The Making of Pig Iron 

The iron that forms the base for all steel, as well as iron, products is 
first obtained from its ores, as a commercial product, from a blast furnace 
similar to that shown in Fig. 1. It is then in the form of an iron that 
contains a large amount of carbon, both in the graphitic and combined 
state. This makes it too weak and brittle for most engineering purposes, 
but about one-third of the total product is run out of the blast furnace 
into pigs of iron that is used only for castings that are to be subjected 
to compressive, transverse or very slight tensile strains, such as bed 
plates or supporting parts for machinery, water pipes, stove plates, car 
wheels, etc. 

The various kinds of steels are relatively increasing in proportion 
to the amount of pig iron used. To-day about two-thirds of this 
product is being turned into steel through purification by either the 
Bessemer, open-hearth, puddling, crucible or electric methods. The 
carbon content is reduced to any desired point, the graphitic carbon 
being eliminated by any of these processes, and the silicon and man- 
ganese are oxidized out by the accompanying reactions, or as a condition 
precedent to the reduction of the carbon. The two impurities of the 
metal which are the greatest bane to engineers and steel makers alike 
are phosphorus and sulphur. These are reduced by either the basic 
open-hearth, puddling, crucible, or electric processes. 

In making steel, the operation begins by making pig iron from the 
iron ore, which is a natural iron rust or a combination of iron and oxygen. 
The oxygen is removed by combining iron ore, coke, and limestone in a 
furnace, as shown in Fig. 2, and heating them to a high temperature by 
injecting superheated air into the bottom of the furnace. The coke is 
burned by the oxygen in the air; a part of it aids in maintaining this 
high temperature while the rest is useful in removing the oxygen from 
the ore. 

This superheated air is usually heated with the gases which have been 
conducted from the top of the furnace to the bottom through the pipe 
shown to the left of the furnace in Fig. 2, and passed through a hot blast 
stove. Four of these stoves are shown grouped in pairs, to the left of 
the blast furnace, in Fig. 1. They are about the same hight as the fur- 

1 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




o 



a 

o3 



m 



o 

l-H 



THE MAKING OF PIG IRON 



^^^ Coke 

Iron Ore 
O Lime 

Drops of Slag 
Drops of Ii-on 
Molten Slag 



=-Sj=_?. Molten Iron 




^iJ- 







ffi 



Fig. 2. — Details of blast furnace. Condition of charge at different 

levels. 



4 COMPOSITION AND HEAT-TREATMENT OF STEEL 

nace, which is something over 100 feet, and are round steel tanks that 
have a comparatively small annular fire-brick chamber in the center for 
nearly the hight of the tank. This chamber is surrounded with brick 
work that is filled with flues. The gas from the furnace comes in at the 
bottom of the central annular chamber; burns on its passage up this; 
comes down through the flues in a heated condition, thus warming up the 
brick work, and then passes out the chimney as waste product. 

When the brick work is heated properly, the gas from the furnace 
is turned off and the blower engine turned on to blow a blast of air through 
the flues into the furnace. This heats the air in its passage up through 
the central chamber and down through the flues, and makes it a hot blast 
when it enters the tuyeres of the furnace. Thus it does not have a coding 
effect on the materials being melted in the blast furnace. Four hot stoves 
are used with each furnace, so that three can be burning gas and warming 
up, while the fourth is having the air blast sent through it into the furnace. 

The gas, which is a product of combustion of the materials in the 
blast furnace, comes down through the pipe A (Fig. 2), which is called 
the downcomer, leaves most all of its accumulated dirt at B, and then 
passes out of the pipe C. 

One-third of this gas is all that is needed to keep the stoves hot and 
the balance was formerly wasted. It is now being sent through gas 
producers, and used to run the blower engine. While the blast furnace 
is thus made to furnish its own fuel for power and heat, it is still sending 
out more gas than can be used for these purposes, and new uses are being 
found for it in other parts of the iron and steel mills. 

The blast furnace is charged from a car that is brought up to the 
top, on an inclined track, with a cable. The charge is dumped from 
the car into the top of the furnace through a hopper and bell. This 
charge consists of coke, iron ore, and limestone, which are dumped into 
the furnace in the order named. The change that takes place in these 
as they pass down through the furnace is plainly shown in Fig. 2. 

The coke serves as a fuel for generating the heat that melts the iron 
ore, and the limestone unites with the earthy materials as the ore is being 
reduced to a molten state. The resultant slag is run off from the top of 
the iron through a hole in the side of the furnace immediately below the 
tuyeres. The metallic iron melts and collects in the hearth below this 
slag, and is tapped out of another hole, close to the bottom. From this 
it is run through channels into molds that form it into "sows" and "pigs," 
or the molten metal is tapped from the furnace into ladle cars as shown 
in Fig. 3, in which it is taken to furnaces for conversion into steel. 

While the metal is in contact with the white-hot coke in the furnace 
it absorbs a certain amount of carbon, some of which is chemically com- 
bined with the iron and another part is held in suspension as graphite. 



THE MAKING OF PIG IRON 




o 






6 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



If the "sows" and "pigs" are cooled slowly it tends to make the carbon 
take the form of graphite. When such iron is broken it has a gray or 
black appearance showing loose scales of graphite, and the iron is soft 
and tough. 

If the metal is cooled quickly, or chilled as soon as it comes from the 
furnace, the carbon has a tendency to be kept in the combined state. 
When fractured such metal will be white and hard. 

Of this product about 20% is made into gray-iron castings, 3% into 
malleable-iron castings, 3% is purified in puddling furnaces to make 
wrought iron, and the balance, or 74%, is converted into steel by the various 




Fig. 4. — Section of sand bed for cast- 
ing pig iron. 

processes. Of the latter 52% is converted by the Bessemer process, 
19% in the basic open-hearth furnace, 2% in the acid open-hearth 
furnace, and 1% by the crucible process. Recently the electric furnace 
has been brought into use, and this promises to take a certain percentage 
for conversion into the finer grades of steel. 

The older method of casting the blast into pigs, and which is used 
now by some, was to have a casting floor in front of the blast furnace 
that was composed of silica sand. In this sand, impressions or molds 
were made for the pigs and these connected with runners called "sows," 



THE MAKING OF PIG IRON 7 

which in turn were connected to a main runner from the furnace. Fig. 4 
shows how the fioor was laid out. In front of and under the tap hole 
of the furnace a small hole, A, was formed into which the iron was run. 
From this the main runner for the iron ran down the center of the cast- 
house. Branching off on either side of this were the sows with the pigs 
leading off from the sows. 

In the main runner, immediately back of each sow, a dam was formed, 
as shown by the two lines at B, and sow C, with its pigs, was run full 
of iron. Then this was dammed and the stream of molten iron turned 
into sow D, which when filled was dammed and the stream turned into 
sow E. This was continued until the whole blast was run off, and then 
the pigs, sows, and runner were broken up, loaded into cars, and the floor 
remolded, ready for the next tapping. At the entrance to each pig and 
at stated intervals in the sows and runner, as shown by the double lines, 
a dam was formed that about half filled these, so as to make the metal 
thinner at this point and thus allow it to be broken more easily into nearly 
standard sizes and weights. 

Automatic machines into which the pigs are cast, cooled, and then 
dumped into cars are now used at most blast furnaces, as the saving in 
labor over the cost of the machine is a big item; the pigs are more uniform 
in size, thus facilitating handling, piling, and storing, and they are free 
from the adhering silicious sand that is especially objectionable in the 
basic open-hearth furnace. 

The pig molding machines are made in several styles, the most com- 
mon forms of which are a revolving frame with the pig molds in a con- 
tinuous series around its annular outer edge, as shown in Fig. 5, and a 
series of molds attached to an endless chain which carries them in a straight 
line from where they are poured to the cars into which they are dumped, 
as shown in Fig. 6. In the latter, the empty molds travel back to the 
ladle underneath the filled ones, and in both the molds are sprayed with 
thick lime water, long enough before they are filled to allow the water 
to be dried out by the heat of the mold, and leave it covered with a coat- 
ing of lime so the molten metal will not stick to the cast-iron mold. 

ELECTEIC BLAST FURNACE 

The experiments that have for some time been carried on for the 
electric production of pig iron seem to be fast approaching a successful 
culmination, and we may in the near future see this method used com- 
mercialljr, especially where an adequate water power is available. 

The Noble Steel Company in California were the pioneer experimenters 
in this country. Their first attempt was a 1500 kilowatt, three-phase, 
resistance type of furnace that was completed in July, 1907, but after 
running it a short time the mechanical difficulties which presented them- 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




THE MAKING OF PIG IRON 



9 



selves made this type of furnace impractical commercially, and it was 
abandoned. 

A 160 kilowatt furnace of a different type was then constructed and 
run for 40 days. From this run data were gathered that were used in 
the construction of the present 1500 kilowatt furnace, shown in Fig. 7. 
The data obtained would indicate that with one ton of charcoal, costing 
about $9, three tons of pig iron could be produced with about 0.25 
electric horse-power-year per ton. 

The quantity of carbon used for the electric smelting of iron ores is 
only about one-third of that required for the ordinary blast furnace. 




Fig. 6. — Double strand, endless chain, pig casting machine. 



Thus charcoal can be used and the product will be charcoal pig iron, 
which, owing to its comparative purity, would demand a higher price 
than the ordinary product. 

In the furnace shown in Fig. 7, the ore with its proper fluxing materials 
is brought in, in cars, and fed into the preheater, A, where it is dried and 
heated by the products of combustion piped from the combustion cham- 
ber of the furnace, B, through the flue, C. After drying it is dumped 
in the scale car, D, which runs around the top of the stack, on a circular 
track, so it can alternately take a charge of ore and flux from A, and 
carbon from the hopper, E, weigh them and charge them into the furnace 
in the proper proportions through the usual hopper and bell in the top 
of the stack. 



10 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Six electrodes (G) are arranged equidistantly around the furnace, 
and the electric current passing through between them melts the charge, 
the metal and slag collecting in the crucible at the bottom of the furnace, 
from which they are drawn as in ordinary practice. All the necessary 
heat is supplied by electrical energy, and thus no blast is blown in. This 
causes all of the solid carbon to be used for reduction, excepting of course 
the small amount that is dissolved into the pig iron. Above the level 
of the charge, however, are small openings at F, for admitting the correct 




Fig. 7. — Electric pig-iron furnace at Noble Steel 
Co., Heroult, Cal. 



amount of air, through valves, to burn the gases that result from the 
reduction of the ores in the lower part of the furnace. 

In Fig. 8 is shown the combination of electric and blast furnace that 
has resulted from several years of study and experiments conducted by 
three Swedish engineers at. the Domnarfvet Iron Works in Sweden. In 
this a large crucible with an arched roof is formed at /. An opening is 
left in the center of the roof, and over it is constructed a stack (J) very 
similar to the ordinary blast furnace; in fact, the only difference being 
that the bosh is contracted more at K, where the charge enters the crucible. 
This was made necessary by the fact that too large an opening would 
not retain the required heat in the crucible part of the furnace without 



THE MAKING OF PIG IRON 



11 



increasing the power to generate the electrical energy to too high a point. 
It was feared that this contraction would result in the furnace clogging 




Fig. 8. — Electric furnace at Domnarfvet Iron Works, Sweden. 

and an overhang form in the bosh, but with a continuous run of three 
months no such condition was apparent. 

Three electrodes (L) that project into the crucible through a water- 



12 COMPOSITION AND HEAT-TREATMENT OF STEEL 

jacketed stuffing-box in the arched roof conduct a three-phase alternating 
current of 40 volts to the charge. The current is from 8000 to 9500 
amperes, and the load 480 to 500 kilowatts. The arched roof over the 
crucible gave considerable trouble in the earlier experiments by being 
overheated, but this is now preserved by taking the gaseous products of 
combustion from the top of the furnace at M, and blowing them back 
through tuyeres at N, which are provided with peep-holes so the roof 
can be examined and the volume of gas increased or diminished as desired. 

In the three months' run, that was terminated July 3, 1909, by the 
general strike in Sweden, it was demonstrated that the electrodes did 
not need readjusting oftener than once a day, and in one case an electrode 
was not touched for five days; that the consumption of energy was 
remarkably uniform even though the short run did not enable the 
furnace to approach its working condition until near the end; that the 
charge moved with regularity into the melting chamber; free spaces were 
maintained underneath the arched roof next to the outer wall, and the 
gases kept the roof effectively cooled. 

This furnace was first constructed as an induction, but was later 
changed to a resistance furnace. It is started and worked the same as 
the ordinary blast furnace, and in the experiments so far only coke has 
been used, but charcoal can be used as well as the "prime ore briquettes" 
and "slig" which they get in Sweden. It has produced 2 tons of iron 
per electrical horse-power-year, but conditions would indicate that this 
could be increased to 3 tons. It being easy to make a pig iron in this 
furnace with a low carbon content, if the molten iron was transferred 
directly to electric refining ftirnaces, it would greatly reduce the time 
consumed in converting it into steel. It now takes a comparatively long 
time to reduce the carbon to the percentage required in the electric con- 
verting furnace when ordinary blast-furnace iron is used. 

The carbon in the experiments with the Swedish furnace averaged 
about 1.80% in the three months' run, while in some previous experi- 
ments it ran as high as 3.20%, and in one tapping it was as low as 1%. 
The silicon varied between 0.20 and 0.07%, but in one case was 4.40%. 
The sulphur content has been as low as 0.005%, with 0.50% of sulphur 
in the coke that was used. 

The ability of the electric furnace to reduce the impurities to a mini- 
mum may result in its becoming a prominent factor in the reduction 
of the ore, and the conversion of this into steel as soon as experience 
teaches the operators to control the carbon and silicon, and it is demon- 
strated that it is practical commercially. In Denmark there will soon 
be started another ore furnace, and in Canada negotiations are well 
advanced for an electric iron-ore reduction and steel plant with a capacity 
of 5000 horse-power. 



CHAPTER II 
Bessemer Process of Converting Iron into Steel 

In converting the blast-furnace iron into steel the Bessemer process 
is the one most used, as it is the cheapest method, although the improve- 
ments in the open-hearth method have been such that it is replacing 
the Bessemer, in some places, for the cheap production of steel, and the 
product which it turns out is much better. 

In the Bessemer process a converter similar to that shown in Figs. 
9 and 10 is used, it being pear-shaped and open at the small end. It 
is hung on trunnions so the metal can be easily poured in and out. Into 
this is poured the melted pig iron, which is usually taken direct from the 
furnace, although it is sometimes remelted, and through this is blown 
cold air in fine sprays in the proportions of about 25,000 cubic feet of 
cold air per minute to every 10 tons of molten metal, which is the usual 
charge for a converter. 

Curious as this may seem to the uninitiated, the cold air raises the 
temperature of the molten metal to such a high degree that it is often 
necessary to inject steam or add scrap to cool off the metal. This rise 
in temperature is due principally to the silicon in the iron which comes 
in contact with the oxygen of the air and produces a state of combustion 
that oxidizes out the silicon and manganese in about four minutes, after 
which the carbon begins to oxidize to carbon monoxide (CO), which 
boils up through the metal and is forced out of the mouth of the converter 
in a long bright flame that gradually diminishes, until at the end of six 
minutes more the carbon has been reduced to about 0.04% and the flame 
dies away. 

Except for the impurities which poison the metal, namely phosphorus 
and sulphur, it has become for all practical purposes a pure metal that is 
very brittle. This makes it necessary to add certain ingredients that will 
toughen, strengthen, and harden it so as to make it useful and workable. 

Carbon is added in different percentages while it is in the molten state 
to give it the proper degree of hardness and strength. 

Manganese is added for the purpose of reducing the sulphur and 
oxygen which the metal has absorbed during the process of conversion, 
as the oxygen would render it unfit for use, and the sulphur if present 
in too large a percentage would make the metal "hot short," and thus 

13 



14 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



difficult to roll or forge when heated. The manganese desulphurizes the 
molten metal by causing a gradual liquefication of manganese sulphide, 




Fig. 9. — Bessemer converter purifying 
the metal. 

which rises to the surface, allowing the sulphur to oxidize into the air. 
Silicon is also added for the purpose of freeing the metal from blow- 



Shoulder 




Fig. 10. — Bessemer converter tilted to pour 
finished metal into ladle. 

holes by reducing the gases, as these work to the top under the influence 
of the chemical action caused by silicon. Of the last two elements but 



BESSEMER PROCESS OF CONVERTING IRON INTO STEEL 



15 



from one-half to two-thirds of the percentages added will be found in 
the finished product, owing to their combining with the impurities and 
oxidizing out with them. 

These ingredients are added to the charge in the converter by first 
mixing them with iron in the proper amounts in a small cupola in the 
converter house, called the spiegel cupola. It is called recarburizing 




Bessemer converters at Lackawana Steel Co. 

the bath. Pig iron high in manganese, called spiegeleisen, is mixed with 
other iron high in silicon and carbon until the right percentages of all 
three are obtained to give the 10 tons of metal in the converter its desired 
composition. After this the converter is tilted, as shown in Fig. 10, and 
the steel poured into ladles. These may be tilting ladles, as shown 
in Fig. 11, or bottom-pour ladles, as shown in Fig. 12. In these, as the 
name signifies, the metal is poured from the ladle by tilting it or through 



16 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



a hole in the bottom. This latter saves turning the ladle over and also 
draws the molten metal away from the slag. From the ladles the metal 
is run into cast-iron ingot molds located on cars, and when they have 
become solid the ingots are often taken to the rolls and rolled into the 
desired shapes while still hot. The ingot molds are usually kept going 




Fig. 11.— Tilting ladles. 

through the converter house in a steady stream; coming in one side 
empty, getting filled and going out the other side. 

Blast-furnace iron with about 1% of silicon is preferred for the Bes- 
semer process, as the lower this is kept the shorter will be the blow, and 
as it is the chief slag producer it will reduce the iron loss by limiting the 
amount of slag made. If too low, however, the blow will be cold and 
take too much time to purify. It is only by working rapidly and allowing no 



BESSEMER PROCESS OF CONVERTING IRON INTO STEEL 



17 



unnecessary wait between blows, thus keeping the converter and ladles very 
hot, that as low as 1% of silicon in the pig iron can be used successfully. 

In the Bessemer process it is almost impossible to reduce the phos- 
phorus, and especially is this so with the acid Bessemer process which is 
the one used in this country. The percentage of phosphorus which goes 
into the furnace in the ore and coke will come out in the finished product 
after it has passed through the converter; hence, it is necessary to use ores 
and coke that are low in phosphorus if a good steel is to be produced. 

In Europe, however, the basic Bessemer converter is used to a cer- 
tain extent. This is the same as the acid, except that the lining of the 



. :if 




Fig. 12. — Bottom-pour ladles. 

furnace is of some basic material such as limestone, containing from 
30 to 40% of magnesia and burned hard, commonly called dolomite. 
The chemical action of this causes the phosphorus to slag off, but ores 
which are low in silicon must be used. 

The Bessemer process being the cheapest way of converting iron 
into steel, all of the cheaper and ordinary grades of steel are made by it, 
such as steel rails, structural shapes, wire, merchant bar, etc. 

Where several Bessemer converters are in operation it takes quite 
a number of blast furnaces to supply them, as it takes two furnaces to 
furnish iron enough for one converter. As the product of each furnace 
is liable to vary in chemical composition, it is necessary to have some 



18 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



means of mixing the product of the different furnaces, before they are 
poured into the converter, if a uniform grade of steel is to be taken out 
of the converter. For that reason a large reservoir, shaped something 
like the housewife's chopping bowl, but with a large spout on it, and 
capable of holding from 200 to 500 tons, is used. Into this is poured the 
metal from the various furnaces and from it are taken the charges for 
the cpnverters. 

This keeps the molten metal continually coming in and going out, 
and it does not get a chance to chill, as there is such a large mass. But 




Fig. 13. — Stripping the mold from ingots. 

should this happen it is supplied with blow-pipes that would l;ring the 
heat up to the proper temperature again. The metallurgist is thus able 
to control the composition to a large degree, as he can order the different 
furnaces to dump in the mixer the amount he desires. In conjunction 
with this he also has some cupolas in which to make any composition 
needed to bring the mixer bath up to the desired standard. 

When the ingots are poured and solidified the molds are at a red heat, 
and it has been a problem to find a metal for the molds that would 
stand the heat. Cast iron is usually used, and it would seem that a prod- 
uct had been found that would prevent their heating up as quicklj^ as 
formerly. Quite recently one of the large mills added about 1% of titanium 



BESSEMER PROCESS OF CONVERTING IRON INTO STEEL 



19 



to their ingot mold iron, and when the ingots were poured it was found 
that the ordinary iron molds were red hot, while the titanium iron molds 
were dark colored. 

As no fuel is used in the Bessemer process of converting blast-furnace 
iron into steel, it has made this the cheapest method of making steel, 
but it also makes the poorest grade of steel, as the phosphorus and sulphur 
are higher than in steels made by the other processes, and the occluded 
gases are not removed to the same extent. 

For the purpose of getting these occluded gases out of the metal a 
new material has been brought into use, in the shape of ferro-titanium, 
that greatly strengthens the metal and increases its wearing quality. 




Fig. 14. — Soaking pit for ingots. 

when used for such purposes as steel rails. This ferro-titanium comes 
in an alloy that is about 15% titanium and the balance pure iron, and 
not more than 1% of titanium is added to the steel. In many cases 
1% will give the desired results, and in some cases 0.40% is satisfactory. 
It is shoveled into the ladle while it is being filled from the converter 
and the ladle allowed to stand for from 4 to 6 minutes so the titanium 
will have time to unite with the oxygen and other gases, for which it has 
a great affinity, and carry these off into the slag. Many steel makers 
will get scared when told to let the ladle stand for from 4 to 6 minutes, 
as ordinarily the metal will chill too much to make good ingots when 
poured, but when titanium is added there is no danger of this, as it raises 
the temperature of the metal in the ladle and at the end of 6 minutes 
it will be as hot, if not hotter, than when leaving the converter. In one 



20 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



case the metal was held in the ladle for from 15 to 20 minutes and was 
still sharp enough to teem successfully. 

Sulphur should be kept low enough in steel rails, as well as in other prod- 
ucts that have to be rolled, for the metal to be rolled successfully and not 
be "hot-short." Sulphur if too high is also liable to cause incipient flaws. 
Phosphorus, on the other hand, if too high makes steel "cold-short," and 
many of the recent railroad accidents that were caused by broken rails, 
especially in cold weather, could be traced to too high a percentage of 




Fig. 15. — Carrying ingot from soaking pit to slabbing mill. 

phosphorus. High-phosphorus rails, however, have good wearing qualities, 
and when titanium is properly added to the molten metal it seems to re- 
move to a large extent the hot and cold brittleness that a comparatively 
high percentage of sulphur and phosphorus give to the metal. 

Many of the fractures in steel rails have been due to miniature gas 
bubbles in the steel, that have, when rolled, produced long microscopic 
cracks and started the fracture; others have been caused by manganese 
sulphide which also rolled out into long cracks; but as titanium removes 
the most of the occluded gases it has overcome these faults and made the 



BESSEMER PROCESS OF CONVERTING IRON INTO STEEL 



21 



Bessemer rails as good if not better than any that have been made by the 
open-hearth process, and the cost has only been increased about $2 per ton, 
as ferro-titanium is not an expensive alloying material. A part of this added 
cost comes from the extra time consumed in allowing the ladle to stand. 
After solidifying the ingot, mold cars are run under the stripper, which 
is located in a tower, as shown in Fig. 13, and from there a long finger 
comes down on top of the ingot to hold it, while two iron loops come down 
over lugs on either side of the mold and lift it off the ingot. The ingot 
is then gripped by a huge pair of tongs on a traveling crane and these 
pick it up and carry it to the soaking pit shown in Fig. 14. If, however, 
the ingot is found to be the proper heat for rolling it is dumped on the 




Fig. 16. — Slabbing mill, 
buggy, which is an iron cart on a track and operated by electricity, and 
carried by this to the slabbing mill where it is automatically dumped 
onto the rolls and the buggy returned for another ingot. 

The ingots are left in the soaking pit until they have attained a 
uniform heat and that is the proper one for rolling, and then they are taken 
out by the ingot carrier, shown in Fig. 15, and laid in the cradle at the 
end of the slabbing mill. This starts them on their journey through the 
roll of the slabbing mill, shown in Fig 16, which is the process whereby 
they are rolled into various commercial shapes. 

It was formerly the custom to roll them into "blooms" or large billets 
about 10 inches square, and reheat again before rolling them into mar- 
ketable shapes, but in the more modern mills the ingots are now taken 
directly to the slabbing mill, which in some cases i-educes their size 1 inch 
at a pass, and there rolled into slabs, that are transferred to other rolls 
that roll them into the desired shape before they get cold. 



CHAPTER III 

Open-Hearth Process for Making Steel 

The open-hearth furnace for converting pig iron into steel is made 
and used in both the stationary and tilting styles, as shown in Figs. 17 
and 18. As the name implies, it has an open hearth on which the metal 
is placed and where it is exposed to a flame which reduces it to a molten 
state; or, in other words, it is openly exposed to the action of burning 
gases. 

This furnace must be a regenerative one to get the high temperature 
that is needed to melt and boil the metal. By this is meant one in which 
the heat carried away by the chimney flue is used to warm the incoming 
air and gas before they enter the furnace. This name has been commonly 
applied to the furnace as shown by the sectional view in Fig. 19, by 
which both the air and gas are heated before entering the furnace by 
sending them through passages filled with bricks which are stacked up 
so as to leave openings between them. Two sets of passages are provided 
so that one can be used to absorb the heat in the exhaust gases while 
the other is warming the incoming air and gas. These passages are 
supplied with reversing valves so that they can be used alternately and 
thus heat the gas and air to a yellow heat before they unite. This 
method gives a very intense heat. 

From 30 to 75 tons of metal are purified in one of these furnaces in 
from 6 to 10 hours. It is then "recarburized," or in other words the 
proper percentage of carbon is added, and the metal poured into ingot 
molds from which it is taken and rolled or forged into the sizes and shapes 
desired. 

As two of the main considerations in the modern steel mill are output 
and economy, the size of furnaces has been increasing and the Talbot- 
Martin open-hearth furnaces have been built with 250 tons capacity, 
while larger ones are to follow. The Martin process consists of connect- 
ing the converters to the blast furnace, and taking the pig iron in a molten 
state to furnaces that convert it into steel as fast as the blast furnaces 
turn it out. This had been proven so economical that all of the large 
steel mills have adopted it. 

The Talbot process changed the stationary furnace of the original 
Martin furnaces into tilting ones so that the excess of slag-forming mate- 

22 



OPEN-HEARTH PROCESS FOR MAKING STEEL 



23 




o 
O 



ui 



pq 



2 



24 



COMPOSITION AND HEAT-TREATMENT OF STEEL 







OPEN-HEARTH PROCESS FOR MAKING STEEL 



25 



rials, that limit the rate of charging and are hard to remove from the 
stationary furnace, can be more easily handled. This made it possible 
for continuous operation, and about one-quarter of the bath is tapped 
off when ready, the balance being recharged with iron ore and limestone 
and reworked. In the tilting furnace a heavier charge could be used, but a 
separate process was required for the final refining. To work this heavier 
charge the resultant slags, rich in iron, would have to be removed to 
permit the final refining and again worked over without loss of their 
iron and heat. This led to the invention of the Martin furnace with 
double hearth, and a tilting device whereby the slag could be poured from 



^._¥ _¥ ¥ ¥ M R 




Fig. 19. — Section through regenerative open-hearth furnace. 



one hearth to the other, as shown in Fig. 20 with a stationary top, and 
in Fig. 21 with a moving top. The stationary furnaces are usually 
charged with a machine similar to that shown in Fig. 22. This moves 
along a track in front of the furnaces and shoves a tray of materials 
into them. 

As opposed to the common form of tilting furnace, the tilting serves 
here not to discharge the furnace, but to carry on different operations 
simultaneously in the one furnace. The amount of tilt given the hearths 
governs the amount of metal or slag to be run from one hearth to the 
other, this amount depending upon the angle of tilt, gradient of hearth, 
length of hearth, and depth of bath. 



26 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




OPEN-HEARTH PROCESS FOR MAKING STEEL 27 

The method of operation in the combined pig iron and ore process, 
which first suggested the furnace, is as follows: A charge is left only suffi- 
ciently long in hearth A to reduce the iron from the slag, this being already 
decarbonized. In order to free the charge from the iron-bearing slag and 
to pave the way for the final refining, the furnace is tilted so the slag 
flows from hearth A to hearth B. After the slag has been poured into 
B, molten pig is charged, the contact of the pig and slag sets up an ener- 
getic refining action and the iron is taken from the slag. Meanwhile 
the charge on hearth A is finished and tapped. The hearth is repaired 
as usual and the tap hole left open. 

As the operation is a continuous one, the slags which have not been 
discharged must be poured when sufficiently low in iron. By a slight 
tilting of the furnace, the slag runs from 5 to A and out through the 




Fig. 21. — Double-hearth furnace with moving top. 

open tap hole. Or it may be discharged over the side walls of hearth B 
and the hearth A used at the same time for charging fresh material. In 
hearth B the heat generated by the decarbonization of the iron is made 
use of by the scattering of iron ore over the charge as long as the tem- 
perature holds. As all of the iron cannot be reduced from the ore, a cer- 
tain amount of ore is slagged. The desired slag, heavy with iron, is 
thus obtained. It will be later poured off into hearth A where the opera- 
tion is steadily going on, molten pig added, and the process continued 
as before. 

Steel is made in two ways with this regenerative furnace: one is called 
the acid open-hearth process and the other the basic open-hearth process. 
About 20% of the pig iron made in this country is converted into steel 
by the basic process, and 2% by the acid. For the making of steel cast- 
ings the acid process was used almost exclusively where open-hearth 
furnaces were used, but these are now giving way to the basic process owing 



28 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



to the fact that ores low in phosphorus and sulphur are becoming higher 
priced each year, and these elements cannot be reduced in the acid furnace. 

The number of charges these furnaces will make into steel before 
having to be rebuilt is about 300 for the basic furnace, which would cover 
a period of from 15 to 20 weeks, and about 1000 heats from the acid open- 
hearth furnace before doing any more to them than the usual patching 
at the end of the week's run. 

Pig iron and steel scrap are the materials with which these furnaces 
are charged, with the addition of enough iron ore to quicken the opera- 
tion. If the percentage of impurities in the raw materials of the charge 
is low the scrap will hasten the process. In Anierica, on an average, 
about one-half the charge is steel scrap but sometimes as high as 90% 



■ '""i 


2 






■ 


iWM 






Hnji^^HWH 


I^^^RpF SH^^^^ 


BI^H^^HHHH@WWB9PB^^^^^''r'^^^^^^^^^^''li 


I ,If^ -1 


t!"/#; 


IfT 


pwpp*r -. 


- _- „ ..^... _jj 



Fig. 22. — - Machine for charging open-hearth furnaces. 

is used. This latter, however, is but little more than a remelting opera- 
tion. In most American mills the steel scrap is first placed on the hearth 
and this then covered with pig iron, as the oxidation of iron is decreased 
while melting by the impurities in the pig iron. In some American and 
most of the English mills the pig iron is put on the hearth first and this 
covered with the steel scrap, with the understanding that the hearth is 
corroded less with oxide of iron, but unless the scrap is small not much 
corrosion will take place. 

In charging the acid furnace it is best to put the scrap on the hearth 
and the pig on top of it, while in the basic furnace we may put in a part 
of the scrap first, the limestone on top of that, then the pig, and cover 
the whole with the balance of the scrap, or we may charge the limestone 
on the hearth, the pig next, and cover the scrap over the top. 



OPEN-HEARTH PROCESS FOR MAKING STEEL 29 

ACID OPElJ-HEARTH 

In this process the metal lies in a pool on the long hearth, as shown 
in Fig. 19, in the same kind of a furnace as the basic, but the lining of the 
hearth differs in the materials used. 

The furnace is lined with silicious materials (sand) for the acid process. 
This lining influences the subsequent operations as the character of the 
bottom determines the character of the slag that can be carried, which, 
in turn, determines the chemistry of the process. The metal is heated 
by radiation from the high temperature of the flame. The impurities 
are oxidized by an excess of oxygen over that which is necessary to burn 
the gas in the furnace. This oxidizes the slag which, in turn, oxidizes 
the impurities in the metal. 

The slag is about one-half silica (SiOo) and the other half is composed 
of oxides of iron and manganese. Nothing is added to form a slag as the 
combustion of the silicon and manganese with what iron is oxidized and 
some sand from the lining in the bottom gives the necessary supply. 

When the metal is melted iron ore is added, and the oxj^gen in the 
ore oxidizes the excess of carbon until the proper percentage is acquired; 
the furnace is then tapped and the proper percentage of manganese is 
thrown into the ladle at the time of tapping. This is in the form of a 
rich ferro-manganese and not in the form of a melted spiegel iron as is 
the general practice in the Bessemer process. 

In the acid process the percentage of phosphorus and sulphur depends 
upon what the stock contains that is put in the furnace, as neither of 
these are removed, but the amount of carbon in the steel, and therefore its 
tensile strength, depends entirely on the conduct of the operation. This 
latter is usually reduced to the right percentage and the charge then tapped 
out, but it may be reduced below the amount required and enough can then 
be added in the ladle to bring the carbon up to the proper percentage. 

The gradual increase in the temperature of the furnace caused by the 
regeneration of the secondary air causes dormant chemical actions to 
be set up. The first effect of this is the oxidation of the silicon, which 
occurs mostly on the surface of the metal, by the oxidizing action of the 
flame. This causes the slag mentioned above to form and cover the 
surface of the bath, thus protecting the metal from any further contact 
with the flame which might cause it to absorb some of the gases, and 
this would be injurious. After the silicon oxidizes out the carbon begins 
to work out by a gaseous action that causes bubbling or boiling through- 
out the bath. By the addition of iron ore this action can be augmented 
as occasion requires. When the carbon has been reduced to the percent- 
age desired, the boil is stopped by deoxidizing agents, such as ferro- 
silicon or ferro-manganese. 



30 COMPOSITION AND HEAT-TREATMENT OF STEEL 

The points in favor of the acid open-hearth process of making steel 
are that the operations are shorter, owing to the fact that the phosphorus 
cannot be reduced and no fluxes are added, except possibly a little silica 
at the beginning to prevent the lining from being cut by the iron oxide; 
the silicon is under direct control; and the bath being more free from 
oxygen at the end of the heat, less trouble is encountered from blow-holes. 

Most engineers and machinery designers agree that acid open-hearth 
steel of a given composition is more reliable, less liable to break and more 
uniform than either Bessemer or basic open-hearth steel, and this is doubt- 
less due to its being more free from the occluded gases, although these 
are not removed as much in the open-hearth as in the crucible or electric 
furnace processes. 

The principal and possibly the only reason this process is not used 
more, and especially in this country, is that ores low enough in phosphorus 
and sulphur are scarce and consequently expensive. As the prices of 
these ores are gradually increasing, and have been for some time, what 
few acid furnaces are now in use are slowly being changed to basic. 

It is usually easy to tell the difference between basic and acid steel, 
but it is difficult to tell the difference between basic Bessemer and basic 
open-hearth steel or between acid Bessemer and acid open-hearth steel. 
Therefore, one has to depend on the honesty of the steelmakers unless 
they wish to go into exhaustive tests of each piece of steel received. 

BASIC OPEN-HEARTH 

A regenerative open-hearth furnace, similar to that shown in Fig. 19 
for the acid process, is used for the basic, but the lining is of a different 
material. It is composed of some basic material that is usually either 
magnesite or burned dolomite. 

The lining or bottom of the furnace takes little part in the operation, 
but determines the character of the slag which can be carried. When 
the bottom is silica (sand) the slag must be silicious and when the bottom 
is basic the slag must be basic. The charge put in the basic open-hearth 
furnace is composed of pig iron mixed with wrought iron, steel scrap or 
similar iron products, the same as in the acid furnace. But in addition 
to this lime or limestone is added, as the silica and the oxides of iron and 
manganese do not make a slag by themselves, and, therefore, must have 
lime to unite with and this gives a basic slag. 

This slag will dissolve all the phosphorus that is oxidized, a thing that 
an acid slag will not do. In the acid open-hearth or Bessemer furnace 
the silicious slag rejects the phosphorus which immediately deoxidizes 
and returns to the iron. Sulphur is also removed to a limited extent, 
and ores with these impurities can be used in the basic open-hearth fur- 
nace, that are not possible to handle by the acid process. When the 



OPEN-HEARTH PROCESS FOR MAKING STEEL 31 

sulphur is high the slag must be charged with all the lime it will stand 
without making the metal infusible and pasty. The slag can contain 
as high as 55% of lime (CaO) for this purpose. If the manganese is above 
1% it makes the slag more fluid and aids in the removal of sulphur. 

If the slag is basic enough not to attack the bottom it will hold the 
phosphorus, providing the stock does not contain over one half of 1%. 
With a higher percentage special attention must be given to the phos- 
phorus to prevent its passing back into the steel when a high temperature 
is combined with violent agitation, as is usual when the heat is tapped. 

A basic slag will dissolve silicon and, although the phosphorus and 
sulphur are lower in the basic steel, the acid steel is considered better, 
owdng to the increased liability of blow-holes and gas bubbles in steel 
converted by the basic process, if the silicon is too low. Then again the 
process of recarburizing sometimes produces irregularities. The metal 
is also more highly charged with oxygen. All of these make a poorer 
quality of steel than is produced by the acid open-hearth process, but a 
far better one than is being made in the Bessemer converter. 

In the purification of the metal the silicon is first almost entirely oxi- 
dized out in the 4 hours or so that it takes the metal to melt, ahd then 
the manganese, carbon, and phosphorus are reduced to a certain extent. 
After this the manganese and phosphorus are reduced to their lowest 
percentages, and lastly the carbon is removed. It is necessary that the 
phosphorus be eliminated before the carbon as the latter protects the 
iron the most and keeps more of it in the bath, thus reducing the loss 
due to remelting. The melter controls this by adding pig iron to increase 
the carbon contents if this is being removed too fast; of if the phosphorus 
is oxidizing out too fast he can add ore to produce the necessary reaction 
to hasten the oxidization of the carbon. 

After being purified the metal must be recarburized to get back into 
it the percentages of the elements that are desired. This must not be 
done when a basic slag is present, or the manganese, carbon, and silicon 
in the recarburizer are liable to cause the phosphorus in the slag to pass 
back into the molten metal. Therefore the recarburizer is added to 
the molten metal as it is flowing from the furnace into the ladle, and the 
slag is allowed to float off from the top. As the spiegeleisen cupola can- 
not be used with the open-hearth furnace, the recarburizer usually con- 
sists of a combination of small lumps of coal, charcoal, or coke in paper 
bags and ferro-manganese. 

When soft steel is being made the carbon in the bath is usually reduced 
to from 0.10 to 0.15%, and enough of the carburizer is then added to 
bring this up to the percentage desired in the finished steel. When high 
carbon steels are being fnade, another method is sometimes used, and 
that is to bring the carbon in the bath just below the percentage desired, 



32 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



and then recarburize up to it. Thus when a 1% carbon steel is to be 
made, the carbon in the bath is reduced to from 0.90 to 0.95%, and enough 
added with the carburizer to raise it to 1%. Many steel makers, however, 
reduced the carbon in the bath to the same point, namely, 0.10 to 0.15%, 
when making both high and low carbon steels, and then get the correct 
percentage by the addition of the proper amount of carburizer. 

Among other open-hearth processes might be mentioned the Monell 
process, in which limestone and a comparatively large amount of iron 
ore are heated on a basic hearth until they begin to melt, and then the 
molten pig iron is poured onto it; the duplex process in which an acid 
Bessemer converter is used to oxidize most of the carbon and the silicon 
and manganese, and the metal then poured into a basic open-hearth fur- 
nace to reduce the phosphorus and the balance of the carbon; the Camp- 




FiG. 23. — One of the largest ingots cast. 

bell No. 1 process, in which a tilting furnace is used for the molten pig 
iron and ore method so the furnace can be tipped backward to prevent 
the bath from frothing out of the door, and the operation continued for 
two or three hours, and the Campbell No. 2 process, which aims to com- 
bine the basic and acid open-hearth processes by working pig iron or 
pig iron and scrap in the basic furnace at a low temperature until most 
of the phosphorus anfl silicon and part of the carbon and sulphur are 
oxidized out, then transferring the bath to an acid furnace and working 
it at a high temperature to remove the rest of the carbon and sulphur. 
The object is to get a low-phosphorus, low-sulphur steel. 

One of the largest ingots that has been cast from the open-hearth fur- 
naces is shown by Fig. 2.3. 

One of the greatest troubles of the steel maker is the pipe that forms 



OPEN-HEARTH PROCESS FOR MAKING STEEL 



33 



in the top of each ingot and forces him to crop off and remelt a large part 
of it. Numerous ways have been tried to overcome this and the most 
successful of these is the fluid compressor of which Fig. 24 is an example. 




Fig. 24. — Machdne for compressing ingots when fluid. 

This consists of a large ingot mold, built in sections, into which the molten 
metal is poured. While the metal is solidifying a ram is pressed down 
into the mold by means of four screws. This compresses the metal as 
fast as it shrinks, and thus removes, or at least partly removes, the pipe 
by not allowing it to form. 



CHAPTER IV 

Crucible Process of Steel Making 

In the crucible process a regenerative furnace is sometimes used sim- 
ilar to the one shown in Figs. 25 and 26. In this the heat does not attack 
the top of the metal as in the open-hearth, but heats crucibles which are 
covered and the cover sealed on with fire clay, so that the gases from the 
fuel will not attack the metal. In some places, however, coke furnaces 
or melting holes containing crucibles are used. 

In Evirope these crucibles are made of fire-clay by the steel makers, 
as they are comparatively cheap and no carbon is absorbed by the metal, 
as is the case with the graphite crucibles used in this country, and conse- 
quently this element can be easier controlled for percentage in the finished 
product. They are usually made to melt 50 pounds of metal in, as that 
is about the limit for the strength of the clay crucible. The molten slag 
on top of the metal cuts deeply into the clay, and the second charge has 
to be cut down to about 45 pounds to get below the slag-line, while for 
a third charge 38 pounds is about the limit, and after this they arc thrown 
away, as it is not economical to use them. One or two steel makers in 
Europe only use the clay crucibles once, as they claim they can get a 
better steel, owing to the larger air space causing greater oxidation and 
the tendencj' of the metal to absorb and occlude some of the gases. 

The graphite crucibles which are used to a large extent in this country 
are made by concerns that make a specialty of this business, and from a 
mixture that is about one-half graphite and one-half fire-clay. These 
generally hold 100 pounds and last for about 6 heats, but as carbon as 
well as silicon are given up by the crucible and enter the molten metal, 
these are more difficult to control than when clay crucibles are used. 

The crucible process is used only for the making of high-grade and 
special alloyed steels, such as high-speed, nickel, or vanadium chrome, 
etc. It is about three times as expensive as the next cheapest, namely, 
acid open-hearth, but for such work as cutting tools, armor-piercing por- 
jectiles, gears that are subjected to heavy or vibrational strains, high- 
grade springs and many other uses the crucible steels far excel anything 
that is made by the other processes. The reason for this superiority 
is largely due to the fact that it is made in covered pots, which exclude 

34 



CRUCIBLE PROCESS OF STEEL MAKING 



35 




36 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



the furnace gases and air. It is therefore freer from oxygen, hydrogen, 
and nitrogen in the form of occluded gases. 

The material used for conversion into steel by the crucible process is 
usually wrought iron and not pig iron as in the Bessemer and open-hearth 
processes. The wrought iron, in the form of muck bars, is cut up into 




I 



Fig 26. — Regenerative gas furnace for crucibles. 

small pieces and placed in the crucible first, and the desired amount of 
carbon is placed on top of it with any other alloying element desired, such 
as tungsten, chromium, manganese, etc. 

In addition to these a little charcoal or pig iron and ferro-manganese 
or spiegeleisen are added. Sometimes a small amount of glass or other 




Fig. 27. — The charged crucible. 

similar material is used to give a passive slag, and various physics, such 
as salt, potassium, ferro-cyanide, oxide of manganese, etc., are used by 
some. The ferro-manganese adds the desired amount of manganese to 
the steel and it is thought that the salt and oxide of manganese make a 
more fluid slag, while the ferro-cyanide might aid the steel in absorbing 



CRUCIBLE PROCESS OF STEEL MAKING 



37 



the carbon. In the pot are also a little air, some slag and oxide of iron, 
this last being the scale and rust on the surface of each piece of metal, 
and silica, alumina, and carbon from the scorification of the walls of the 
crucible. Sometimes different amounts of cheaper steel scrap is mixed 
with the wrought iron, but this always lowers the quality of the finished 
steel. A crucible that has been charged and is ready for melting is showTi 
in Fig. 27. 




Fig. 28. — Pouring ingots from crucibles. 



Some time is required for the reduction of the silicon from the slag and 
lining as well as for the various reactions which occur. When this reduc- 
tion has reached a point where the steel contains from 0.20 to 0.40% 
of silicon and the metal lies quiet and "dead," that is, the evolution of 
the gases have stopped so it will pour quietly and cast into solid ingots, 
the crucible is taken from the furnace and the contents poured into ingot 
molds, as sho'WTi in Fig. 28. After these have cooled they are usually 



38 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



reheated in a furnace and reduced to a size suitable for rolling by hammer- 
ing under a steam hammer, as shown in Fig. 29. This reduces the grain 
and makes the metal more dense. 

Crucible steel usually contains less than 0.40% manganese, more than 
0.20% silicon, less than 0.025% phosphorus, and less than 0.030% sul- 




FiG. 29. — Hammering the ingot. 



phur, while the carbon content is usually made high, owing to the uses 
to which crucible steels are put. 

The main difficulty with this process is in making large ingots so these 
ingredients will be combined in a homogeneous mass. As the personal 
element is a factor in the charging of the crucibles, and these hold only 
100 pounds or less, the steel made in each crucible is liable to vary some 



CRUCIBLE PROCESS OF STEEL MAKING 



39 



in the composition of its ingredients. Thus when a 1000 pound ingot is 
to be cast it requires 10 or more crucibles to fill it and the metal does 
not have a chance to mix thoroughly before getting cold, which will result 
in certain of the ingredients showing a higher percentage in some part of 
the ingot than in others unless great care is exercised in charging each 
of the 10 crucibles. 

A large part of the crucible steel is hammered into bars, as shown in 
Fig. 30, and the accuracy and quickness with which a hammersman can 
turn out these bars is one of the surprising features of the steel business. 




Fig. 30. — Hammering octagon bars. 



They usually work by the ton, and it is difficult for the inexperienced man 
to tell the bars from rolled stock. 

This process has changed very little in the last 100 years or more, 
and its chemistry, which consists principally of eliminating the slag in 
the wrought iron an(i adding carbon silicon and manganese to the metal, 
is very simple. The progress which has been made in crucible steel 
is due almost entirely to the discovery of new alloying materials that have 
added strength, toughness, wearing qualities, cutting qualities, etc., 
to the metal. Thus more different kinds of good steels, and l^etter 



40 COMPOSITION AND HEAT-TREATMENT OF STEEL 

steels, are being made to-day by this process, which is way above all 
the other processes for making steel of quality, than at any time previous. 
The enormous and wonderful change that has been made in the steel 
business is due entirely to the perfecting of methods and machinery for 
making steel quicker, cheaper, and in larger quantities. This has been 
accomplished, but when a fine grade of steel is required the crucible process 
has to be used in practically the same manner as did our ancient ances- 
tors. The progress that has been made in electricity and the experi- 
ments that have been carried on with the electric refining furnace, however, 
would seem to indicate that in the not very distant future this might do 
away with the slow, laborious, and costly crucible process; if not entirely, 
at least to a large extent, 

WROUGHT IRON 

The wrought iron used in making crucible steel or for other purposes 
is also made by the same process and in much the same manner that it 
was 100 or more years ago. A reverberatory furnace hearth is "fettled" 
or lined with oxide of iron, that is either good iron ore, roasted puddle 
cinder, or roll scale. On this, pig iron is melted, which throws off some 
of the manganese and silicon, and a slag with a high content of iron oxide 
is formed by absorbing this element from the lining. The impurities 
are then removed to a more or less extent by reducing the heat and set- 
ting up a reaction between the carbon, manganese, silicon, sulphur, and 
phosphorus in the molten iron and the oxide of iron in the slag. This 
basic slag and the iron oxide lining carry the oxygen to the impurities 
and cause them to oxidize out of the metal, and they may be assisted by 
the excess of oxygen in the furnace gases. 

As the iron approaches nearer to puritj^ it thickens, as the purer the 
iron the higher will be its melting temperature, and the heat in the fur- 
nace is not sufficient to keep it molten. When it reaches a pasty state 
the charge is rolled into balls, called puddle balls, that average about 
150 pounds apiece. From the puddle furnace these balls are taken to 
a rotary squeezer that kneads and squeezes out a large amount of slag 
or they are taken to a drop hammer where the slag is hammered out. 
The balls are then rolled into bars, which removes more of the slag, 
leaving the rolled bars containing from 1 to 2%. These flat bars are then 
cut up into short lengths and form the muck bar used in making crucible 
steel. 

Sometimes in this country and as a general thing in Europe, the 
squeezer is not used, in which case the puddle ball is worked under a 
hammer or "shingled" to remove the slag and weld the particles of iron 
in the ball together. Puddling and shingling being extremely hard and 
hot work, however, efforts are continually being made to devise machines 



CRUCIBLE PROCESS OF STEEL MAKING 41 

that will do the work. The rotary squeezer does that part of the work 
cheaper than it can be done by hand labor, and many different kinds 
of automatic puddling furnaces have been designed and built. With 
these latter the finished product has not been turned out as good, as yet, 
as it can be made by the same hand labor that our remote ancestors 
used. The results obtained, however, with the mechanical furnace, have 
nearly reached those desired, and may yet be in their entirety. 



CHAPTER V 

Electric Furnaces for Steel Making 

The electric furnace has been brought into quite prominent use in 
the last few years for the making of steel. In certain ways this has i^oved 
itself to be a commercial success, while in others it is still in the experi- 
mental stage, but from the present progress (August, 1910) in the art 
it would look as though the electric furnace was destined to supplant 
the expensive crucible method of steel making, and if electricity could 
be obtained cheap enough it might even be a strong competitor to the 
open-hearth method. 

When a good ore can be procured the electric furnace can produce 
a metal with a higher degree of puritj^ than any of the other processes, 
owing to the absence of the sulphuric gases. Mr. Harbord, the Canadian 
government expert, said, "Steel equal in all respects to the best high- 
grade Sheffield crucible steel can be produced in the electric furnace at 
a less cost than by the ordinary crucible methods." 

The high temperature insures extreme deoxidization of the steel and 
a vigorous oxidization of the impurities can be employed in the electric 
furnace. It cannot eliminate arsenic and copper, but it practically elim- 
inates phosphorus and sulphur, and thus removes the injurious effects 
of these. The sulphur is oxidized but until only a trace is left and the 
phosphorus remains in the metal only in very small percentages. For 
the high-grade steels such as tungsten, nickel, nickel-chrome, self-hardening 
and high-speed tool, which are made out of blast-furnace products and 
scrap it has given good satisfaction in several steel plants in Germany, 
France, Sweden, and Italy. 

STASSANO REVOLVING FURNACES 

In the Stassano furnaces, shown in Fig. 31, that are being operated in 
Turin, Italy, the heat is generated by three electrodes which come together 
in the center of an enclosed furnace immediately over the metal. This 
furnace is also mechanically revolved in order to agitate the metal and 
thus accelerate the chemical reaction and reduce the time of operation 
to a minimum. It is also built without the revolving mechanism for 
some uses. 

42 



ELECTRIC FURNACES FOR STEEL MAKING 



43 



The electrodes are cooled by water-jackets that surround them on 
the ' outside of the furnace, and the cylindrical melting chamber is 
enclosed so that the atmosphere throughout it will be neutral. The 




•Stassano revolving thermo- 
electric furnace. 



material treated is not in contact with the electrodes or other material, 
and therefore its composition is not subjected to any alteration, as the 
furnace only furnishes the heat to produce the reaction between the 
substances in the charge, and does not introduce other elements. 



44 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




ELECTRIC FURNACES FOR STEEL MAKING 45 

Among the different oxides contained in commercial iron ore that of 
iron is the first one which is reduced. The remaining oxides (SO2, MnO, 
MnOa, CO, MgO, etc.) are, therefore, left without reducing elements, 
and hence forced to pass, with the assistance of the flux, into the slag. 
In the same way, if pig iron or iron scrap is used, mixed with slag-forming 
materials, the pig iron and impure iron may be successfully refined in the 
same furnace, and this is accomplished by starting from predetermined 
quantities without any tests during the process. 

The reducing element that is used for absorbing the oxygen of the 
iron oxide is the carbon of common coal or of charcoal, which is the purest 
of all fossil fuels. When refining pig iron or impure iron, oxide of iron 
must be added, which may be natural or artificial (hammerslag) or powder 
of rusty scrap. To make the slag, the common fluxes, used in metallurgy, 
are suitable and may be selected according to convenience and special 
requirements. Since the atmosphere in the furnace is chemically neutral 
and the operation can be carried out for any length of time desired, the 
metal can be freed almost entirely from its impurities without the risk 
of harmful oxidation. 

Refined iron may be obtained direct from the ore in this furnace if 
it is charged with iron ore mixed with a reducing agent and the proper 
fluxes, in the correct proportions, to transform the gangue into a slag of 
a composition that will absorb the impurities in a single operation. Such 
a charge, being gradually heated with the exclusion of air, cannot absorb 
oxygen from it, and the flux maintains its quality at a rising temperature 
so that it is able to perform its mission when the right temperature has 
been reached. 

HBROULT FURNACE 

The Heroult furnace, as shown in Fig. 32, is but a modified open- 
hearth, with the heat introduced above the metal by the electric cm-rent 
in place of gas; no electrical parts being in the furnace proper. Thus 
the bottom and side can be patched as fast as they may be burned away 
without interfering with the work of the furnace. 

In the later types of Heroult furnace the heat is introduced by means 
of two electrodes working in series; the current passing through the bath 
from one electrode to another, and vice-versa. The power being the 
same in both cases, this necessitates carrying only one half the current 
that would be needed if the current flowed from one electrode through 
the bath, and thence through a plate contact in the bottom of the furnace, 
as shown in Fig. 33. 

In this case the heat is generated in the slag and not in the metal 
itself; thus making the slag the hottest part of the furnace, so that all 



46 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



impurities can be removed by the use of special slags. The poorest kind 
of scrap can therefore be used, as the sulphxir and phosphorus are both 
removed at a low cost, and the metal can be converted into the finest 
grade of tool steel. 

In a 5-ton furnace starting on cold materials one ton of metal can 
be melted and partiallj^ refined, with 600 kilowatt-hours; for the finish- 




FiG. 33. — Heroult resistance furnace. 



ing slag 100 more would be necessary, making 700 kilowatt-hours all 
told. In a 15-ton furnace these figures would be considerably reduced. 
If molten metal is charged into the 5-ton furnace and this only needs to 
be deoxidized, desulphurized, and recarburized, it will take from 140 
to 160 kilowatt-hours, and for a 15-ton furnace this would probably 
be cut down to about 100 kilowatt-hours. In cold melting and continu- 
ous work the consumption of electrodes is from 60 to 65 pounds for each 



ELECTRIC FURNACES FOR STEEL MAKING 47 

ton of steel, which includes the waste ends of the electrodes. When molten 
metal is charged into the fm-nace, this consumption is only from 10 to 
15 pounds per ton of steel. The electrodes just touch the flux covering 
the molten metal and can be operated automatically or by hand. 

About the best lining for this furnace is good magnesite mixed with 
basic slag, with tar for a binder; burnt dolomite can also be used success- 
fully. The furnace can be lined by any one who can make a good bottom 
in a basic open-hearth furnace. The lining is never exposed to silicious 
slags, and can be repaired after each heat by simply throwing in mag- 
nesite or dolomite, as the case may be. This should make it last a long 
time, and with the furnace run with due care, one year is not too long 
for it to last, although furnaces have had to be relined in three months. 
The roof is damaged the most, and this usually has to be replaced once 
a month. For that reason an extra roof is kept on hand so the change 
can be made in a few hours. 

Two 15-ton Heroult furnaces are now being used by the United States 
Steel Corporation (August, 1910), and this is about the largest size that 
can be successfully operated when two slags are used, owing to the difficul- 
ties that might be encountered in raking the first slag off the molten metal. 
The first slag used being an oxidizing one to remove the phosphorus, and the 
second deoxidizing for the removal of the sulphur and the gases. It is the 
intention to build 30-ton furnaces, however, where only one slag is used. 

The detrimental features of this style of furnace, which are yet to 
be overcome, are the high electrode costs, and the possibility of increasing 
the carbon contents of the finished metal. For melting purposes as in 
steel foundry work it is also difficult to choose a suitable protective flux, 
that will act as a heating medium, and still not act on the ingredients of 
the molten metal. 

KELLEE FURNACE 

The Keller furnaces are more or less of the Heroult type, but differ 
in constructional details. These are shown by Fig. 34, which is a sec- 
tional elevation. As will be seen, the carbon electrodes A are massive 
and are lowered into vertical shafts that are separated but connected below 
by a lateral canal B. The electrodes are surrounded by the raw material 
in these vertical shafts, and the electrical current passes from one elec- 
trode to the other, down through this material and through the lateral 
canal, in which it becomes molten. The molten metal is then drawn off 
by tapping. A central electrode is located at C. This furnace is well 
adapted for making steel castings, and it can be cleaned by dumping the 
bottom D. When thus used a central stack is added to the furnace 
shown, that feeds the raw material into the vertical shafts surrounding 
the electrodes. 



48 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




Fig. 34. — Keller electric steel furnace. 



ELECTRIC FURNACES FOR STEEL MAKING 



49 



KJELLIN AND COLBY FURNACES 

Resistance furnaces of the induction type were invented by Mr. 
E. A. Colby, in the United States in 1887, and independently reinvented 
by Dr. Kjellin in Sweden twelve years later. As a natural sequence a 
combination was formed and the patents of both are used on the same 
furnaces. 

In Fig. 35 is shown the principle on which this simple induction fur- 
nace is built. It is in realitj' a transformer, in which the l)ath of molten 




Fig. 35. ^ Kjellin induction furnace. 



metal forms the secondary circuit. The magnetic circuit C is built up 
of laminated sheet iron like the core of a transformer. The primary cir- 
cuit is a coil D, consisting of a number of turns of insulated copper wire 
or tubing surrounding the magnetic circuit. The ring-shaped crucible 
A, made of suitable refractory materials, also surrounds the magnetic 
circuit, and when filled with molten metal forms the secondary circuit 
of the transformer. The annular crucible is supplied with cover K. 
When the coil D is connected with the poles of an alternating-current 



50 COMPOSITION AND HEAT-TREATMENT OF STEEL 

generator, the current, when passing through the coil, excites a varying 
magnetic flux in the iron core and the variation in the magnetic flux induces 
a current in the closed circuit formed by the molten metal in the crucible 
A. The ratio between the primary and secondary current is fixed by the 
number of turns of the primary, and the magnitude of the current in the 
steel is then almost the same as the primary current multiplied by the 
turns of the j^rimary coil. Thus, in a small furnace of this type a current 
of 500 volts and 280 amperes supplied to D induces a current of seven 
volts and 20,000 amperes in the metallic bath. 

In this style of furnace the charge may be either in the hot molten 
state or in the form of cold scrap, pig iron, etc. When the latter materials 
are charged one or more metal rings, made of cast iron, wrought iron, or 
steel, must be placed in the hearth A to complete the electrical circuit 
and start the melting. When molten metal is charged, this of itself 
forms the circuit, and for continuous working it is customary to leave a 
sufficient amount of metal in the crucible A to establish the bath. 

If the charge is made with molten metal a saving in time and power 
is effected in refining the bath. When scrap and pig iron is charged, 
the metal ring must be put in and the current turned on until this is melted 
down. The charge is then gradually added and melted until the full 
charge is obtained. After this the temperature is raised to any desired 
point and the necessary additions made to give the required percentages 
of carbon, manganese, nickel, chrome, tungsten, etc., according to the 
kind of steel that is to be produced. 

This kind is primarily a melting furnace, and the best results are 
obtained in melting high-grade materials. As a commercial substitute 
for the crucible method it has several advantages: High and easily con- 
trolled temperatures are attainable, as the temperature is directly depend- 
ent upon the primary circuit; the process is clean and gases cannot attack 
and injure the bath; "overkilling" is practically impossible and a saving 
in labor is effected. A furnace that will produce 1000 tons of steel per 
year can be easily handled by three men and a boy per shift. 

A Kjellin induction furnace is shown in Fig. 36, as it is tapping 1000 
pounds of tool steel into a ladle for pouring into ingot molds. This fur- 
nace is hung in a frame on trunnions, and is tilted when it is necessary 
to pour off the heat, by the aid of gears, electrically operated by a 
switch from the furnace platform. 

One of the difficulties encountered with furnaces of this style, the 
hearth of which is in the shape of an annular ring, is caused from what 
is commonly known as the "pinch" phenomena. When an alternating 
or direct current passes through a liquid conductor, the electromagnetic 
forces tend to contract that conductor in cross-section. This contrac- 
tion is apt to localize itself at some certain spot and form a depression 



ELECTRIC FURNACES FOR STEEL MAKING 



51 



in the molten metal that gives it the appearance of being pinched by an 
invisible force. 

This force is a function of the current, and size and shape of the cross- 
section of molten metal, and is independent of the resistance, voltage, 
watts, temperature, heat, length of channel, etc., except where changes 
in these effect the other quantities. Involved in the actual contraction 
is also the smoothness of channel, viscosity, fluid friction, weight of float- 
ing masses, etc. 

The contracting force is small for a current with relatively low den- 




FiG. 36. — Kjellin induction furnace tapping 1000 pounds 
of tool steel. 

sities, but when these become higher the force is great enough to contract 
the cross-section of molten metal to zero and thus rupture the circuit. 
When increasing currents are small the level falls slowly at first and then 
more rapidly. When a certain unstable level is reached the contraction 
becomes very rapid for the same increments of current. There is also 
a certain critical current at which rupture might take place immediately. 
Into the depression formed is liable to drift the more refractory, solid, 
floating materials that will prevent a reunion of the molten metal and 
cause a freezing of the charge before they can be removed. When this 



52 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




ELECTRIC FURNACES FOR STEEL MAKING 53 

occurs it is difficult to start the current flowing again so as to melt the 
metal, and the furnace usually has to be taken apart and rebuilt. 

The "pinch" need not be feared in low current density furnaces, 
except when other causes might produce local contraction, as it only 
takes place at relatively high current densities. But when it does occur 
it means a frozen charge or a broken core, unless the separated metal 
can be quickly brought together by opening the external circuit for an 
instant and then follow it by a reduce current. 

A positive limit, above which the current and thus the temperature 
cannot go, is fixed by the critical current. This limit is greater with a 
greater density, lesser viscosity, deeper channel, more regular and smoother 
channel, and a molten metal surface that is freer from heavy floating 
masses. 

BOCHLING-RODENHAUSER ELECTRIC FURNACE 

The Rochling-Rodenhauser furnaces, of which one of the 8-ton 
furnaces is shown in Fig. 37, consists of the same arrangement of trans- 
former and primarjr coils as is shown in the Kjellin furnace. In addition, 
however, it has a number of steel terminal plates embedded in the lining 
and these are connected to a few heavy turns of copper, placed outside 
the primary coils, that collect and feed the induced current in these turns 
to the terminal plates. 

These are, therefore, termed combination furnaces, and are designed 
to suppress the magnetic leakage that would occur in large furnaces of 
the simple induction type; the auxiliary turns being located in close prox- 
imity to the primary coil and magnet core. The total result is that the 
main hearth can be made of much larger cross-section, and a good power 
factor can be obtained even in l)ig furnaces without the use of a current 
of such low periodicity as was necessary with the original induction fur- 
naces. 

This furnace is built for single-phase or three-phase currents ; the three 
phase being more suitable for large quantities of metal and for large daily 
outputs at a normal periodicity. The principles on which these furnaces 
are built can be seen in Figs. 38 and 39. 

In Fig. 38, H H are the two legs of the iron core of the transformer. 
They are surrounded by primary coils A, connected with the alternating- 
current generator. Through the action of the currents in the primary 
coils, secondary currents are induced in the two closed circuits formed 
by the bath; these two circuits being connected so that the whole looks 
like the figure 8. The primary coils are so arranged that the induced 
currents in the common part of the two circuits, that is, between the 
legs H H oi the iron core, have the same direction. 

So far the furnace acts like two combined ordinary induction furnaces. 



54 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



The difference consists in the use of extra secondary coils B B, surround- 
ing the primary coils A A. From these secondary coils the currents 
are conducted to metallic plates E. The plates are covered by an elec- 




c-d 




Fig. 38. — Outline sections of single phase. Combination furnace. 

trically conducting mixture of refractory material G, that forms part 
of the lining of the furnace. 
, The currents from the secondaries pass from the plates E, through 



ELECTRIC FURNACES FOR STEEL MAKING 



55 



the lining G, and then through the main hearth D of the furnace. The 
channels C only act as conductors for the secondary currents induced 
in the bath. In the main hearth D we thus have the currents from the 
channels C C, and also from the extra secondaries B B. 

The construction of the three-phase furnace is practically the same 
as that of the single-phase, except that a third transformer is added and 
therefore only a plan view is shown in Fig. 39. 

The amount of extra power that can be given to the furnace by means 
of the extra coils is of course not unlimited, because increased power 
means increased current, and consequently increased current density 




Fig. 39. — Plan view of 3-phase furnace. 



in that part of the lining that conducts the current to the steel. This 
current density must not be driven too far, because the heat evolved when 
the current passes the lining will increase as the square of the current, 
and too high a current density would therefore result in the destruction 
of the lining. 

This is the reason vf\\y a combination of induced currents and currents 
taken from the extra coils must be used. It would not, for the reason 
stated, be possible to conduct all the amount of current through the 
lining that is necessary for the working of the furnace, not to speak of 
the pinching effect that would very probably cut off the current at the 
contact between the steel and the lining, if the current density in the 
lining were driven too far. 



56 COMPOSITION AND HEAT-TREATMENT OF STEEL 

The Rochling-Rodenhauser furnace was designed for refining fluid 
Bessemer steel from the converter, in order to produce a higher quality 
of steel rails than before, and also with the intention of making high- 
class steel in general. 

For refining purposes the furnace is worked in the following manner: 

After tapping, fluid steel, from the converters, is poured into the fur- 
nace, and suitable materials — burnt limestone and mill scale — for 
forming a dephosphorizing basic slag are added. When the reactions 
are ended this slag is taken off by tilting the furnace. For making rails 
the phosphorus is brought down sufficiently low in one operation, but 
for the making of the highest class of steel the operation has to be repeated. 

When the phosphorus is removed, the carbon in the steel (if carbon 
steel is made) is adjusted by adding pure carbon to the bath, and after- 
wards a new basic slag is formed in order to remove the sulphur. This 
slag is also formed of burnt lime, sometimes with the addition of fluxes 
such as fluorspar. 

One necessary condition for successful desulphuration is that the 
slag is free from iron, and therefore sometimes ferro-silicon is added in 
order to quicken the reduction of the iron in the slag. How far this 
refining will have to be carried naturally depends on the quality of steel 
wanted. By repeated refining operation with fresh slag, the phosphorus 
and sulphur can be brought down to an exceedingly low percentage, but 
this refining, of course, takes a longer time and consequently more electric 
energy per ton of finished product. 

GIROD ELECTRIC STEEL FURNACE 

From the numerous experiments that have been carried on, has been 
deduced the fact that the best method of insuring practical success in. 
the operation of electrical furnaces is to so design them that they will 
have the utmost simplicity in the construction of the necessary apparatus. 
Until the Girod furnace was perfected the Heroult was the simplest and 
to this was due its success, but now (June, 1910) the Girod heads the 
list of electrode furnaces in simplicity and safety in construction and 
operation. 

The owners of the process are ready to guarantee the successful work- 
ing commercially of a 25-ton furnace for refining steel previously made 
molten in a Martin furnace. While this is a cheaper method of produ- 
cing a good grade of steel than that of melting down the raw materials 
in the electric furnace and then refining it, Mr. Paul Girod, the inventor 
of this furnace, claims that steel cannot be produced from a molten 
charge that has the same good quaHties as that made exclusively in the 
electric furnace from pig iron, scrap, etc. Such quaHties, for instance. 



ELECTRIC FURNACES FOR STEEL MAKING 



57 




58 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



as resistance to shock; and in tool steels, hardness, tenacity, and durability 
after hardening. In this Mr. Girod is supported by others. 

In Fig. 40 is shown a 12-ton Girod furnace as it is pouring the charge 
into a ladle by tilting. To the right of this will be seen another furnace; 
the picture being taken at the steel works started by Mr. Girod a few 
years ago in Ugine, Savoie, France. This company has a good water- 




FiG. 41. — Plan and sectional elevation of 12-ton Girod electrical furnace. 



power for generating their electricity, and are to-day (June, 1910) 
operating 19 electric furnaces, with from 400 to 600 electrical horse-power 
each, while 12 new furnaces are being constructed that will consume 1200 
horse-power each. All kinds of steel are being made, from structural 
up to high-speed tool steel. 

The construction of this furnace can be seen by a study of Fig. 41. 



ELECTRIC FURNACES FOR STEEL MAKING 



59 



While it is classed with the electrode furnaces it is in reality a combination 
of the resistance and arc heating and seems to work as well in large units 
as in small ones. One or more electrodes A according to the size of the 
furnace, are lowered through a hole, or holes, in the cover that is lined 
with silica brick, and the metal M, which is from 12 to 14 inches deep, 
serves as the opposite electrode. The current passes from electrode 
A, in the form of an arc, into the slag S, where a large amount of heat 
is produced, then into the metal M, and finally out through the contact 
pieces C to the current conductor. If a number of electrodes are used 
above the bath they are in parallel. 

The most important principle in the Girod process is the effective 





Fig. 41a. — Operating principle of Girod furnace. 

manner in which the electric current is made to pass through the molten 
metallic body and cause it to become an important heat producer. 

Water is driven through a passage about 6 inches deep in the outer 
end of each contact piece C, so as to cool them and aid in regulating 
their temperature and resistance. The length and cross-section of the 
contact pieces are such that each will take up only a certain part of the 
whole current and thus none become overheated and greatly increase 
in resistance. They are made of pure iron to avoid any deterioration 
of the furnace charge, and are not only connecting rods between the 
furnace charge and the current generators, but also serve as regulating 
current distributors, by making the electric charges pass uniformly from 



60 COMPOSITION AND HEAT-TREATMENT OF STEEL 

and to the centrally hanging carbon rod or rods in radial direction to 
and from the periphery of the bath. This is important, not only for 
uniformly heating the bath, but also for keeping every part of the liquid 
metal in constant motion. This movement accelerates the contact 
between the impurities of the iron and the refining slag swimming on 
top of the bath. 

In operating on cold materials the electrode is lowered until it rests 
upon the heap of scrap; then the current finds no other way out than by 
means of numerous small arcs through the whole mass of material, thus 
breaking it down simultaneously in all parts of the hearth, with no stick- 
ing of cold pieces to the bottom. When feeding cold scrap one does not 
put in the whole charge at once. After the larger part of the charge has 
been deposited upon the hearth, the current is sent through the heap 
as described; then the rest of the charge is put into the furnace, together 
with the first batch of the refining ingredients. Taking the run of a 
2-ton furnace as an example, the charge consists of 4500 to 5500 pounds 
of iron scrap, and the first batch of refining slag usually consists of about 
175 pounds of lime (CaO) and 500 pounds of iron oxide ore. Together 
with the iron oxide that covers the scrap, the iron ore serves as an oxidi- 
zing agent. 

The smelting of the iron charge and the first batch of refining slag 
requires i^ to 5 hours. As the slag becomes exhausted of iron oxide 
and therefore of its oxidizing power, samples are taken and tested to 
ascertain the degree of refinement of the molten metal. According to the 
degree of purification, the furnace now receives (after the first slag has 
been skimmed off) a second, and if necessary a third batch of lime-iron- 
oxide slag. After the removal of the last slag the surface of the metal 
bath is thoroughly cleansed by throwing in about 75 pounds of lime and 
skimming this off after a while. The further treatment of the bath depends 
upon the impurities which could not be removed by the lime-iron-oxide 
refining, and upon the quality of steel to be produced. Thus deoxidizing 
or other refining agents are employed; such as, ferro-mangano-silicon, 
ferro-aluminium-sihcon, ferro-mangano-aluminium-silicon, and other alloys. 

The final step in the production of special steels is the addition of 
iron alloyed with metals like nickel, tungsten, chromium, and others, after 
these refining operations. 

A removable cast-iron frame is fitted to the cover, and this contains 
water-jacketed ports through which the electrodes enter the furnace. 
While the metallic frame is not necessary it serves a iiseful purpose by 
stiffening the cover and keeping air from entering the furnace and attack- 
ing the bath. As the electrodes have the same polarity, when more than 
one is used, there is no danger of short circuits through the metal frame 
and collars and across the cover. The electrodes are easily regulated 



ELECTRIC FURNACES FOR STEEL MAKING 61 

automatically by feeding from the generator, on the voltage, in the single 
electrode furnaces, or on the intensity of the current when this is fed by 
a transformer, or several electrodes are supplying current equally. The 
electrode consumption is about 38 pounds in 2-ton, and 31 pounds in 
12-ton, furnaces per ton of steel produced. 

Two 2|-ton Girod furnaces that are in use in France and Belgium, 
are shown in Fig. 42. One of this style is used in Switzerland for steel 
castings only. 

SUMMARY 

Many others have been and are experimenting with electric furnaces 
in the hope of improving them and cheapening their operation, among 
which might be mentioned Gustave Gin, Marcus Ruthenburg, E. A. 
Greene, F. S. McGregory, Prof. B. Igewsky, and others, but none of 
these have as yet passed the experimental stage, and been put to prac- 
tical use. Horace W. Lash, of Cleveland, Ohio, U. S. A., has developed 
a process that is applicable to the electric furnace, but as it is also appli- 
cable to the open-hearth process it cannot be classed with the purelj^ elec- 
tric steels. 

Some years ago Mr. Lash became interested in the direct production 
of steel from the ore, and made experiments. The outcome of this was 
a compromise between the direct and refining methods. He found that 
when an intimate mixture of iron ore, carbon, fluxes, and cast-iron borings 
was heated, a reduction took place; by proportioning the mixture properly, 
steel of the desired grade could be produced and practically the whole 
of the iron in the mixture recovered as good steel. 

A typical Lash mixture is as follows: Granulated pig iron, or cast- 
iron borings, 23%; iron ore, 60%; coke, 11%; lime, 6%. To reduce this 
in the open-hearth furnace required the addition of pig iron or scrap. 
A typical charge for 100 tons of steel ingots being: Lash mixture, 122 
tons; pig iron, 32 tons; ore, 2 tons. In the electric furnace pig iron or 
scrap is not necessary, and for 100 tons of steel ingots the charge would 
be, Lash mixture, 172 tons; ore, 2 tons. 

The experiments proved that a superior quality of steel was obtained; 
the cost of its production was in general lower than when the regular 
methods of making steel were used; and that the electric furnace was 
the best method for the process. Companies have been organized in 
Cleveland and Canada for making steel by the Lash process. 

That the electric furnace will produce as high, if not a higher, grade 
of steel than is produced by any of the other methods has been fully 
established; that it is cheaper than the crucible process, and may in time 
equal the open-hearth, is also pretty well recognized. That magnetite 
and hematite ores can be economically smelted; that sulphur and phos- 
phorus can be reduced to a few thousandths of a per cent, even without 



62 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



manganese; that the percentage of siUcon can be altered at will, and that 
ores containing titanic acid up to 5% can be refined in the electric furnace, 
make of it one of the coming factors in the manufacture of steel. 




Fig. 42. — 2| ton Girod furnaces in use in France and Belgium. 



In two steels of the same composition, 1 inch square, one of which 
was made in the electric furnace and the other in a crucible, a considerable 
difference in torsion was noted. The electric steel was twisted cold until 
it looked like a corkscrew, while the crucible steel only took half as many 



ELECTRIC FURNACES FOR STEEL MAKING 63 

twists before breaking. A Bessemer steel has been made better by merely 
submitting it to the heat in an electric furnace for a short time. In another 
case, a tool-steel maker found that he could produce his tool steel with 
smaller additions of silicon and manganese than was necessary in the 
crucible process. 

The only explanation that appears probable is that the higher heat 
and reducing, rather than oxidizing, atmosphere of the electric furnace, 
expels some of the gases that are dissolved in the steel, and possibly aids 
the removal of the combined oxygen, thus making the deoxidation more 
complete than in the crucible. 

The latest development in the electric furnace experiments has been 
the combination gas and electric heated furnace. As the United States 
Steel Corporation have an unlimited supply of natural gas in their plants 
in the Pittsburg district, they have built a tilting open-hearth furnace in 
which a cold charge is melted down with gas, after which it is turned 
off and electrodes lowered into the metal, through the top of the furnace, 
to refine the charge. 

This is apparently the most economical method of making electric 
steel that has yet been suggested, as the natural gas can be obtained for 
less than 20 cents per thousand feet, and at this rate is much cheaper 
than electricity, and perhaps just as good for melting down the charge. 
The use of the electric current can then be confined to removing the 
impurities from the bath. This, however, is in the experimental stage 
and what the cost of operation will be, on what quality of steel can be 
produced, has not yet been established. 



CHAPTER VI 
Ingredients of and Materials Used in Steel 

The elements entering into the composition of steel have been studied 
and investigated in many ways and their effects have been carefully 
noted. Many new alloying materials have been brought into use in 
the past few years. These were made available by the high temperature 
obtained in the electric furnace, as this enables them to be separated 
from the elements with which they were found, and combined with iron 
to make ferro-alloys that could be added to the steel in its making. Many 
other elements are being experimented with, and some of these give prom- 
ise of adding new properties to steel or bettering the properties already 
recognized as good ones, and thus we may be able in the near future to 
still further improve it in quality. 

These new alloying materials have given us steels which, for strength, 
cutting qualities, wearing qualities, and ability to withstand vibrational 
and torsional stresses, attain a higher standard of excellence than would 
have been considered possible a short time ago. 

CARBON in steel 

Of all the alloying elements entering into steel, carbon is the most 
important, as it is the quantity and condition of the carbon in the metal 
that makes the distinction between iron and steel. The distinctive fea- 
tures of different grades of steel are due more to the variation of the car- 
bon contents than to the differences in any or all of the other elem.ents. 

One of the wonders of metallurgy is the effect that a small per cent, 
of carbon has upon iron. Pure iron, that is, iron that has been electro- 
lytically deposited, has a tensile strength of 4500 pounds per square 
inch, and if we add a few tenths of 1% of carbon, the tensile strength 
immediately raises to 60,000 pounds per square inch or more. This is 
a quantity so small that it is out of all proportion to the mass in which 
it is distributed. 

Carbon unites with chemically pure iron in all proportions up to 4 J 
per cent. The capacity of the iron for carbon can be increased by using 
manganese and when a high percentage of manganese is added to steel 
the carbon content can be raised to 7 or 8 per cent. Manganese, sili- 
con, phosphorus, sulphur, etc., may vary widely in quantity, but the carbon 

64 



INGREDIENTS OF AND MATERIALS USED IN STEEL 65 

usually decides the class in which the steel belongs; for the carbon gives 
greater hardness and strength to the steel, with less brittleness, than any 
other element. 

To get the desired percentage of carbon into steel, various methods 
are used. In the melting in process, that is, adding the carbon to the 
steel when the metal is molten, the Bessemer, open-hearth, and crucible 
processes all use a different method. Besides this, there is the cementa- 
tion process in which the carbon is put into the steel while in a solid state. 
Several methods are employed in this, and they consist of submitting 
the metal to the action of some carbonaceous material in the presence 
of heat. 

In the Bessemer process, the charge of molten metal is put into the 
converter and blasts of air are blown through it from the bottom of the 
furnace. These blasts of air raise the temperature, cause the metal to 
boil, and oxidize out all of the silica, manganese, and nearly all of the 
carbon. The charge is then recarburized until the proper percentage 
of carbon and other ingredients are obtained, after which the metal is 
cast into ingots. 

In the open-hearth process, the charge usually consists of 50% pig 
iron and 50% of scrap, and these are melted up together. The pig iron 
usually contains from 3| to 4% of carbon, and the charge is melted down 
and boiled until the carbon has been reduced by oxidation to the required 
amount. Tests are taken every half hour or so, to determine when the 
carbon has been reduced to the proper percentage, and when this is reached, 
the ferro-alloys are added to the bath and it is cast into ingots. 

In the crucible process, muck iron and charcoal is charged, the crucible 
sealed up and the charge melted down. If the muck iron contains 0.10% 
of carbon, 100 pounds of muck bar and 15 ounces of charcoal, which is 
the form in which the carbon is put in the bath, will make a 1% carbon 
steel. With the muck iron higher or lower in carbon, the charcoal is 
diminished or increased to obtain the correct carbon content. 

By the cementation process muck iron is changed iiato blister bars, 
or from a low to a high carbon metal by placing alternate layers of iron 
and charcoal in a furnace and covering the top with clay to prevent the 
charcoal from burning off. Much iron containing about 0.10% of carbon 
is usually used. By closing the furnace, heating it up slowly for a few 
days and then keeping it at a good yellow heat for about nine days, the 
iron has absorbed about 1% of carbon. This product is often used for 
making crucible steel by merely melting it down in the pot and adding 
the alloying materials that are desired to purify and strengthen the 
metal. This process is also used in Harveyizing armorplate, but in this 
case but one plate aiad one laj^er of charcoal is used, and about 30 days' 
time consumed; ten of which are used to slowly heat the metal up to the 



66 COMPOSITION AND HEAT-TREATMENT OF STEEL 

desired temperature, at which it is retained for ten more days, and the 
final ten days are consumed in allowing it to slowly cool. With this 
treatment the carbon has penetrated to a depth of from 1 to li inches 
and the surface of the plate will show about 1.00 per cent, of carbon 
when analyzed. 

The Krupp process conducts illuminating gas over the surface of the 
armorplate instead of the charcoal. When the plate is at a good yellow 
heat, it decomposes this gas into carbon and hj^lrogen; the carbon being 
deposited on the plate in a finely divided state as soot, which is imme- 
diately absorbed by the metal, while the hydrogen escapes as a gas. 

Both of these cementation processes are used with various modifica- 
tions for carbonizing small pieces in special furnaces, and this subject 
is treated in detail under the chapter on Carbonizing. A low carbon 
iron or steel will absorb carbon from any carbonaceous material in the 
presence of heat; in fact, if two pieces of metal are heated to the proper 
temperature, one containing a high and the other a low percentage of 
carbon, the carbon will flow from the high to the low point. Its action 
under these conditions is very similar to the difference in potential of 
an electric current, which always flows from a highly charged body to 
that of a lower, until an equilibrium has been established. 

The actual mode of existence of the carbon in the metal is of great 
importance in the working and treating of steel, and several words have 
been coined to define the different conditions of these. Ferrite means 
carbonless iron, and its chemical abbreviation is Fe. Cementite con- 
sists of three atoms of iron combined with one atom of carbon, FesC. 
Graphite is the carbon that is uncombined, as, when an excess of carbon 
is present in iron, all that vnW combine will be taken up by the iron and 
form cementite, while the balance will remain in a free state or graphitic 
carbon. Pearlite is alternate layers of ferrite and cementite, and Auste- 
nite is a solid solution of carbon in iron. Martensite, Troostite, Sorbite, 
etc., are transition forms that are taken up under the chapter entitled 
"Hardening Steel." 

As an illustration for better understanding what solid solution means: 
if you will put a small amount of salt in water, the two will combine into 
a transparent mass, and it is not possible to distinguish one from the 
other by any means except separating them; thus it forms a solid solu- 
tion. If, however, we keep adding salt, there comes a time when it will 
not all combine with the water, and flakes of it can be seen in suspension 
or gathered around the edges or settled on the bottom. This is similar 
to the graphitic carbon, or the carbon that will not combine with the 
iron. 

In heating and cooling steel, the carbon assumes different forms, as 
well as when in different percentages. In Seating and cooling a piece 



INGREDIENTS OF AND MATERIALS USED IN STEEL 



67 



of steel that contains 0-90% of carbon or less, it goes through the changes 
graphically illustrated in Chart 1. With a steel containing not more 
than 0.90% of carbon, it is almost impossible to develop any graphitic 
carbon, as this is a eutectic steel that contains about six times as much 
pure iron by weight as the weight of the cementite, and thus it is almost 
impossible to force the carbon into the graphitic state. The ability to 
produce graphitic carbon is greatly decreased as the carbon lowers in 
percentage. 

Starting with a soft or annealed bar of steel at atmospheric temper- 
ature, which has been designated zero on the chart, the temperature will 
rise uniformly until it reaches a point at about 1300° F. Here the tem- 



tCensUe Stt-ength. 
IBBOF.AcS 



ArsKOOr. 




A 1-2 1360 X. 



ISOOF. 
Acl 



1250 F, 
Arl 



Lowest Tensile Sti-ength 

Chart 1. 



perature hesitates and remains stationary until certain internal condi- 
tions have been satisfied, when it again rises uniformly to about 1400° F., 
where the second transformation takes place in the metal, and the tem- 
perature again remains stationary until this has been completed, and 
it again rises uniformly to about 1550° F., where the third change takes 
place. These have been designated the recalescent points, and they 
have been named Acl, Ac2, and Ac3. If suddenly cooled at the upper 
point, the steel will be made very hard, and the metal will be held in 
the condition it was placed by the applied heat. 

If allowed to cool slowly or annealed, the temperature will drop uni- 
formly until slightly below the temperature at which the transformation 
took place while the heat was rising, or about 1500° F., and the metal 
will then slightly rise in temperature. This point has been designated 



68 COMPOSITION AND HEAT-TREATMENT OF STEEL 

Ar3. When the alterations in the structure and grain have been com- 
pleted, the temperature again falls uniformly until it reaches a temper- 
ature of about 1350° F., at which point the second change takes place, 
that is the opposite of that on the rising temperature, and has been desig- 
nated Ar2. After the change has been completed at this point, it again 
lowers in temperature uniformly to the next point, or Arl, at about 1250° 
F., and after this change takes place, it then gradually lowers to atmos- 
pheric temperature. These have been named the decalescent points. 

At the atmospheric temperature, the carbon in this steel is in the 
cementite form, or FesC. When it is heated up to Acl, the heat that 
has been absorbed by the metal causes a partial decomposition to take 
place that results in the dropping of one atom of iron, and when the metal 
has completely assumed the form of Fe2C, the temperature rises to Ac2, 
where it drops another atom of iron and the carbon assumes the form of 
FeC. With this change completed, the temperature again arises to Acl, 
where the carbon goes into solid solution with the iron or the Austenite 
form. 

On slowly cooling the metal from this point, the reverse action takes 
place, that is, at ArS the carbon absorbs one atom of the iron that has 
been dropped on the rising temperature, and the metal becomes FeC; 
while at the next point, or Ar2, it absorbs the second atom of iron that 
was dropped and takes the form of Fe2C, while at Arl it absorbs the 
third atom of iron and again becomes FesC, or cementite. 

During these changes in the metal, the iron assumes three different 
conditions. While the temperature is rising up to Ac2 it is highly mag- 
netic, and has been called alpha (a) iron. At Ac2 it loses its magnet- 
ism and between Ac2 and Ac3 it is as non-magnetic as brass, and has 
been called beta ()8) iron. This change in magnetism is accompanied 
by a change in electric conductivity and specific heat. At Ac3 another 
change in electrical conductivity takes place and also in the metals 
crystalline form. Above Ac3 it is called gamma (y) iron. 

The carbon content of steel usually varies between 0.10 and 2%. 
Metal having more than 2% is called cast iron and used as such, as but 
little more than 2% of carbon can be retained in the metal m a combined 
state, without a large part of it forming into graphitic carbon. Wrought 
iron is about the only useful iron product that contains less than 0.10% 
of carbon, but this is made by a working instead of a casting process. 

With a carbon content of from 0.10 to 0.30%, steel is soft and cannot 
be hardened enough to prevent cutting with a file. It is then called 
machinery, soft, or low carbon steel. With a carbon content of from 
0.30 to 2% it can be hardened so as to cut other steels or metals, and is 
then called tool, half hard, hard, or high carbon steel. Exceptions to 
the above statement may be made in hard steels, as a low carbon steel 



INGREDIENTS OF AND MATERIALS USED IN STEEL 



69 



can be made hard by either manganese, tungsten, or chromium, but it 
is true of soft steel. 

Every increase in the percentage of carbon increases the hardness 
and brittleness, and therefore its Uabihty to fracture when cold or when 
heated suddenly, while it reduces the elongation and reduction of area. 
The tenacity shows a gradual relatively quick rise up to 0.90% of carbon, 
and a slow rise from there to 1.20% carbon, after which it decreases. 
The relative ductility decreases in an irregular curve with an increasing 
carbon content. These properties are more graphically shown in the 
chart (Fig. 43), while the separation of the ferrite and carbon and the 
formation of graphitic carbon is shown by Fig. 44. 



Percentage of Carbon 
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s 

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§ 65,000 

& 

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j(of Ferrite 100 

Fig. 43 



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Effect of carbon on physical properties of steel. 



The strength of steel is always secured at the sacrifice of some other 
desirable property, but the sacrifice is less in the case of carbon than with 
any other element. The tensile strength and elastic limit are raised con- 
siderably by hardening, and the higher the percentage of carbon the greater 
the degree of hardness that can be attained. But the greater the cai-bon 
content the less will be the elongation, as hardened high carbon steel 
is very brittle. This brittleness makes high carbon steel very easily 
damaged in heat treating or working, and the carbon content is usually 
kept as low as possible for the strength and hardness that is desired. 
"Sudden rupture" is a term which is especially applicable as a character- 
istic of carbon steel products, and a large amount of effort is being expended 
to discover either new ingredients, new methods of manufacture, or new 
ways of treating the metal that will overcome this characteristic. 



70 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Some investigations that have been carried on prove that beginning 
with pure steel, which has a tensile strength of 40,000 pounds per square 
inch, every increase of 0.01% of carbon, up to about 1%, increase the 
strength of acid open hard steel about 1000 pounds, and basic open 
hard steel 770 pounds per square inch. As the color method of deter- 
mining the carbon content does not show all the carbon present, these 
figures, however, should be changed to 1140 and 820 pounds respectively, 
when the color method of analysis is used. 




0.5 1.0 1.5 3.0 2,5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 

Percentages of Carton 

Fig. 44. — Effect of temperature on carbon. 



Probably Bessemer steel would show lower figures than this and 
crucible or electric steel higher figures. This is doubtless due to the fact 
that some processes of steel making remove the oxides and occluded 
gases better, or to a greater extent, than others, and it has been pretty 
well demonstrated that these are injurious to the strength and life of 
steel. Other things might enter into the manufacture of steel that would 
alter these figures, but with all other conditions equal they will probably 
hold good. 



INGREDIENTS OF AND MATERIALS USED IN STEEL 71 

That the maximum strength is placed at about 1% carbon is probably 
due, to a great extent, to the fact that the crystalline constituents form 
an intimate mixture near the eutectoid proportions, and hence the crys- 
tallization is very small comparatively. With more carbon (cementite) 
present the pearlite grains are surrounded with a network of cementite, 
while with less the pearlite grains are surrounded with a network of 
ferrite, and both of these decrease the cohesive force inherent in the metal, 
and therefore have a weakening effect. 

One of the oldest theories as to what made high-carbon or tool steel 
harden was that, the carbon in unhardened steel was partially in the 
graphitic and uncombined form, and when it was hardened all the carbon 
assumed the combined form. The evidence to prove this theory was 
that when hardened steel was dissolved a flocculent graphitic carbon 
could be found in the insoluble residue, but when hardened steel was 
dissolved no such element could be found, as a definite carbide (FeC4) 
is formed. This certainly aids in the support of this theory and makes 
it sound reasonable. 

MANGANESE 

Manganese occurs in nature principally in the form of manganese, 
dioxide (Mn02), which is commonly called black oxide of manganese, 
but occasionally is it found in other compounds, such as braunite, man- 
ganite, carbonate, etc. Some of its compounds with oxygen and hydrogen 
are distinctly acids while others are distinctly basic, and it is in connec- 
tion with the base-forming elements that it is of interest in steel making. 
For use in steel making the dioxide is separated from its oxygen, in the 
presence of charcoal, by employing high temperatures in an electric fur- 
nace. It looks like cast iron, is brittle and hard, and is combined with 
iron, to form ferro-manganese. Sometimes silicon is added to form ferro- 
sili con-manganese . 

Manganese is an element that is always found in steel, but its true 
properties and effects were not known until about twenty years ago, 
when they were discovered by R. A. Hadfield, a metallurgist and steel 
maker of Sheffield, England. Its effect when added to steel up to 2% 
with various percentages of carbon is best shown by Fig. 45, the actual 
mode of existence of the carbon in the steel being very important. 

When more than 2% and less than 6% of manganese is added, with 
the carbon less than 0.5%, it makes steel very brittle, so that it can be 
powdered under a hand hammer. From 6% of manganese up, this brittle- 
ness gradually disappears until 12% is reached, when the former strength 
returns and reaches its maximum at about 14%. After this a decrease 
in toughness, but not in transverse strength, takes place, until 20% is 



72 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



reached, after which a rapid decrease again takes place. Manganese 
may affect the tensile strength and ductility of steel, either indirectly 



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Fig. 46. 



9 10 11 12 13 14 15 16 17 18 19 20 

Percentage of Manganese 

Eifect of Manganese above 6 per cent. 



Fig. 46 shows the effect of more than 6% of manganese on the 
tensile strength and elongation. 



INGREDIENTS OF AND MATERIALS USED IN STEEL 73 

Steel with from 10 to 15% of manganese and less than 0.50% of car- 
bon is very hard and cannot be machined or drilled in the ordinary way; 
yet it is so tough that it can be twisted and bent into peculiar shapes 
without breaking. This makes a steel that is only suitable for casting 
into the desired shape. A process has recently been patented however, 
for casting this steel into ingots, and then subjecting them to a heat treat- 
ment that enables them to be mechanically worked; that is rolled, forged, 
etc., and this might possibly be extended to machining operation. 

Manganese in the form of a ferro-alloy containing about 80% of man- 
ganese is added to a heat of steel at the time of tapping, so that it may 
seize the oxygen which is dissolved in the bath and transfer it to the slag 
as oxide of manganese. Manganese prevents the coarse crystallization 
that the impurities would otherwise induce, and steels low in phosphorus 
and sulphur require less manganese than those having comparatively high 
and percentages. 

Manganese has a greater affinity than iron for both sulphur and oxygen, 
and therefore is used in steel making for a desulphurizer as well as a dioxid- 
izer. This it does by forming a maganese sulphide (MnS), or a man- 
ganese oxide (MnO), and these are taken off in the slag. About four 
times as much manganese is needed as there is sulphur present, as it does 
not always catch all of the sulphur to affinitize with; thus if any great 
amount of sulphur or even phosphorus is present a considerable amount 
of manganese is desired to counteract the effect of these. If the bath 
is kept liquid enough and enough manganese is present, no oxygen or 
sulphur will be found combined with the iron, and if these are not carried 
off in the slag they are very injurious to the metal. The length of time 
and the care required, however, make it commercially impractical to 
reduce the oxygen and sulphur to a trace in this way. Therefore man- 
ganese is used to reduce them to commercial percentages, and other mate- 
rials are used to still further remove them for the finer grades of steel. 
Manganese sulphide will probably weaken steel more than any other 
impurity if segregated together with phosphide of iron, especially if the 
metal is rolled, as this magnifies the sulphide by spreading it out during 
rolling. 

Manganese is not only useful to cleanse the bath of impurities, but 
it has other properties that aid in making steel better. The amount 
that can be left in the steel varies with the amount of various other ingre- 
dients that are added to the metal, and this is especially so of carbon. 
In effect it behaves in practically the same manner as carbon, as also 
does nickel. With a given carbon content the introduction and increase 
of manganese causes a series of structural changes similar to those that 
occur in carbon steels, that only contain small percentages of manganese. 

While the action upon iron of these three elements is of the same kind, 



74 COMPOSITION AND HEAT-TREATMENT OF STEEL 

it is not of the same strength, as the equivalent of 1% of total carbon, 
that contains the maximum amount of hardening carbon, is 7.25% of 
manganese and 17.55% of nickel. All three of these cause a structural 
change in the metal from pearlite, that includes the sorbitic, to marten- 
site, that includes the troostitic, and then to the polyhedral structure, 
and with none of them is a special carbide formed. Chromium has an 
analogous effect, but not as complete, as a double carbide of iron and 
chromium forms and this is not maintained in solution in the iron without 
tempering. 

The critical temperature to which it is safe to heat steel is raised by- 
manganese, owing to its resisting the separation of the crystals in cooling 
from liquid, and conferring the quality of hot ductility. It also assists 
in producing more uniform alloys, and tends to make steel crystals smaller 
by making the metal plastic, and thus counteracting the tendency toward 
crystallization that phosphorus causes, although the metal is more liable 
to crack when heating or suddenly cooling it from a red heat. The good 
qualities more than offset the bad, and it is a very useful factor in steel 
making if the proper percentages are used. It atones for many evils 
in steel by healing it up and producing a smoothly rolled surface. 

In the ordinary steels this percentage is usually from 0.70 to 1.00%, 
while in many of the special alloys it runs from 0.30 to 0.50%. In the 
high-speed steels the manganese content is from 0.10 to 0.30%, and in 
steels for carbonizing this should be kept below 0.20%. The ductility 
which it gives to steel, especially when added in the percentages above 
the zone of brittleness, is decidedly affected by the rate of cooling. In 
this it works in the opposite way to carbon; slow cooling, making man- 
ganese steel brittle, while quick cooling makes it extremely ductile. 

A peculiar fact that was brought out by some experiments was that 
a pure nickel-iron alloy that contained from 12 to 13% of nickel was 
highly magnetic, but by the addition of 5% of manganese this metal 
became as non-magnetic as brass. While manganese steels are known 
to be non-magnetic, it was not known that manganese would have this 
effect upon nickel, which also makes a non-magnetic steel when added 
in certain proportion. 

To sum up, manganese alloys with iron in all ratios, it being reduced 
from its oxides at a white heat by carbon, and thus its presence increases 
the power of carbon to combine with iron at a very high temperature 
(about 2550° F.), and almost entirely prevents its separation into graphitic 
carbon at the lower temperatures. Manganese permits a higher total 
carbon by raising the power of saturation, and it is easily separated from 
iron by oxidation, as it is even oxidized by silica. While it does not coun- 
teract the cold shortness caused by phosphorus, it does prevent the red 
and yellow hot shortness caused by sulphur, by removing, reducing, or 



INGREDIENTS OF AND MATERIALS USED IN STEEL 75 

counteracting the effect of iron oxide, silica and the siHcates, phosphorus 
and copper, and by the prevention of ebulUtion during soUdification and 
the formation of blow-holes. 

Manganese retards the formation of blow-holes, though not to the 
extent that silicon does, by preventing the oxidation of carbon, and thus 
the formation of carbonic oxide. This it does by increasing the solubility 
of the gases that are dissolved in the steel when it is molten and retained 
in it while solidifying. It probably raises the elastic limit and slightly 
increases the tensile strength; adds fluidity to the metal; increases hard- 
ness; furnishes fusibility when present in considerable quantity, and 
gives greater i^lasticity and mobility to the metal at forging heats. Some 
recent investigations, however, make it doubtful that it diminishes 
ductility to any extent. 

SILICON 

Silicon is the second most important element in the solid part of the 
earth's crust, oxygen being first, and forms 27.21% of it. It is never found 
in the free state in nature, but, having a powerful affinity for oxygen, it 
occurs chiefly as silicon dioxide (Si02), which is commonly called silica, 
and in the form of silicates in combination with oxygen or such metallic 
elements as sodium, potassium, aluminum, and calcium. Silica will 
neutralize every base it comes in contact with when molten, and all metal- 
lurgical slags are the silicates thus formed. The silicon used in steel 
making has to be separated from the oxygen of the silica and united with 
iron to make ferro-silicon. Sometimes manganese is added to this to 
form ferro-silicon-manganese. 

Many contradictory statements have been made as to the effect of 
silicon on steel. When the silicon is left in the pig iron from the blast 
furnace, it is an indication that the metal has been blown too hot, and as 
the iron has not been completely converted into steel the metal has a 
brittle character. The percentage varies considerably, according to the 
heat of the charge, and this causes irregularities which may account for 
the difference of opinion. To get the best results in the steel the silicon 
should be eliminated as much as possible from the iron and a definite 
quantity added in the form of high percentage ferro-silicon, or ferro- 
manganese-silicon. This gives a very different effect from that of silicon 
left in the blast-furnace iron. 

If silicon is added to steel in such a manner as to cause it to enter 
into solution as silicide, it confers upon the metal valuable properties; 
but if it forms a silicate it is injurious in many ways, even to the point 
of being dangerous. This latter seldom occurs, or at least occurs only 
to a slight degree, as the silicates of iron, manganese, etc., dissolve into 
each other very readily and form a slag; although manganese silicate 



76 COMPOSITION AND HEAT-TREATMENT OF STEEL 

probably occurs more frequently and causes more failures in steel than 
is generally supposed. 

Silicon, having a great affinity for oxygen, it seizes this wherever found, 
and carries it off into the slag, whether in the form of gases, oxides, or 
dissolved oxygen. This prevents the formation of blow-holes, and makes 
the steel harder and tougher. Thus it is better able to withstand wear 
or crushing from continual pounding. This is only so, however, when 
the silicon has been eliminated as far as possible from the pig iron and 
now added to the steel bath in the form of ferro-silicon or silicon spiegel. 
Otherwise the steel is liable to show brittleness and irregularity of per- 
centage. 

One steel maker found that if the percentage of manganese was 5.2 
times the percentage of silicon, and the multiplicand made to equal a 
percentage in the steel of 2.05, the metal would be entirely free from blow- 
holes, but the pipe would be large; if the total was made to equal a 
percentage of 1.66, the pipe would be smaller and numerous minute 
blow-holes would appear, but not enough to harm the steel for the use to 
which it. was to be put. He also found that 0.0184% of aluminum would 
give the same result as the 1.66% of manganese and silicon. 

In the Bessemer converters the silicon increases the temperature of 
the bath, which gradually decreases as it is blown out. Thus the lower 
the percentage of the sihcon in the pig iron the shorter will be the blow, 
and below 1% of silicon is dangerous, as it does not give time enough 
for the removal of the impurities. At the end of the blow, 0.2% of silicon 
is added to rid the bath of the gases. Thus the percentage of silicon is 
usually under 0.2 in Bessemer steel, and for steel rails many engineers 
are limiting it to 0.1%. 

During the "killing" in the crucible process the steel absorbs silicon 
from the crucible and thus becomes sound by throwing off the gases. 
The graphite crucibles used in this country give up more silicon than the 
clay crucibles used in Europe, and consequently allowances have to be 
made when charging. Too long "killing" makes the steel harsh, l)rittle, 
and weak, owing to its absorbing too much silicon, which is liable to be 
retained in steel in the form of silicates. Crucible steels nearly always 
contain- more than 0.2% of silicon. 

The influence of silicon on the results of quenching is similar to that 
of carbon in many ways. It is also dependent upon the coexisting amount 
of carbon and manganese. It neutralizes the injurious tendency of man- 
ganese, and it is difficult to obtain silicon in steel without the presence 
of manganese. 

An increase in the percentage of silicon slightly raises the tensile 
strength and lowers the elongation and reduction of area. Up to a con- 
tent of 4%, silicon increases the tensile strength about 80 pounds per 



INGREDIENTS OF AND MATERIALS USED IN STEEL 77 

square inch for every 0.01%. Beyond this amount a weakening of the 
metal seems to take place. Without a considerable percentage of man- 
ganese, silicon steels show very low shock resistance, whether annealed 
or quenched. With 0.20% of silicon the tensile strength is increased 
about one-third more than 0.01% of carbon would increase it. Beyond 
a content of 5%, sihcon steels are but little used for structural purposes. 

Steels containing a little less than 1% of carbon and from 1 to 2% 
of silicon, have been used quite successfully for hard-tool steels. Below 
a content of 1% silicon ceases to have an influence on quenching and the 
metal may be classed as a special carbon steel. Some makers of steel 
try to keep the silicon as low as possible, but many of the best steels 
contain from 0.20 to 0.80%. With the carbon content low the silicon 
may be raised to a fairly high figure, but with the carbon high the silicon 
should be kept low. It should also be kept low when the phosphorus is 
high. 

Silicon steels are extremely fibrous with a remarkable resistance to 
shock in the direction of lamination, but practically no resistance in a 
direction perpendicular thereto. This quality makes them especially 
adapted for leaf springs. 

Ferro-silicon, as now made in the electric furnace, with a silicon con- 
tent between 30 and 60%, is very brittle and liable to disintegrate spon- 
taneously, even though made of comparatively pure material. With 
the silicon in any percentage from 30 to 40 and 47 to 65, it gives off 
quite large quantities of phosphorated hydrogen gas, especially when 
attacked by moisture in any form. The phosphorated hydrogen is gen- 
erated from calcium phosphide, which in turn is largely formed from the 
calcium phosphate that is present in quartz and anthracite when they 
are submitted to the high temperatures of the electric furnace. Smaller 
amounts of arseniureted hydrogen are also evolved, and both of these 
are highly poisonous. They are present in the ferro-silicon in the form 
of occluded gases. When it disintegrates, the amount evolved is greater, 
owing to the largely increased surface that is exposed. 

Many damaging and fatal accidents by explosions and poisoning 
have been caused from these gases since ferro-silicon has been manufac- 
tured in the electric furnace. Most of these have occurred when ship- 
ping it on boats, as there is then more moisture to attack it. When the 
silicon content is below 30 or above 65% these gases do not appear to 
evolve in amounts that are dangerous. As it is not really necessary to 
use the alloys between these percentages for the manufacture of any of 
the iron products, unless it be for basic furnace steel, their use, if not 
their manufacture, should be prohibited. Where absolutely necessary to 
use them, the ferro-silicon should be broken up into useable sizes and 
completely exposed to the air for at least one month before shipping. 



78 COMPOSITION AND HEAT-TREATMENT OF STEEL 

It should then be stored in a place where there is plenty of ventilation 
to carry off the gases. Ferro-silicon made in a blast furnace, however, 
does not give off any of these gases, and there is a movement started in 
Europe by the electric furnace ferro-silicon makers to abandon the 
manufacture of this alloy in the dangerous percentages. 

PHOSPHORUS 

Phosphorus always occurs in nature in the combined condition, and 
unites with metals to form phosphides. It forms two oxides, namely, 
P2O3 and P2O5, and also forms compounds of the same character and sim- 
ilar composition to arsenic, antimony, and bismuth. It is consequently 
placed in the same chemical group as these. 

It is always encountered in reducing iron ores, and is a very difficult 
element to remove entirely from the finished iron and steel product. In 
these materials it must be reduced to as low a percentage as possible, 
as phosphorus is without doubt the most injurious element that is found 
in steel, notwithstanding the fact that in the past many experiments have 
been carried on that apparently proved that phosphorus, up to about 
0.12%, strengthened steel. When these same steels were put into actual 
use, however, failures occurred, and the cause was nearly always traceable 
to the phosphorus. 

In the rolling mills phosphorus does not show any bad effect, as the 
heat under which the steel is worked seems to overcome this, but when 
the metal has become cooled and is subjected to sudden shock or to vibra- 
tional stresses, it breaks very easily. The lower the temperature and the 
higher the phosphorus the easier will the breaks occur. This has led to 
the term, "cold-shortness," as applied to the effect of phosphorus on 
steel. 

Phosphorus diminishes the ductility of steel under gradually applied 
load as shown by the reduction of area, elongation, and elastic ratio when 
specimens are pulled apart in the ordinary static strength testing machines. 
But when the steel is tested in the rotary or alternating vibrational testing 
machines, as well as with a pendulum impact machine, the decrease in 
ductility and toughness is shown to a greater degree. Phosphorus also 
reduces deflection, and the rigidity thus imparted might be considered 
an advantage for structural purposes, although even this is doubtful 
owing to the metal's weakness at low temperatures and when subjected 
to shocks. 

Phosphorus steels are so capricious that they may show a reasonably 
high static ductility and still show very brittle when shock tests are applied. 
Therefore the safest rule to apply is to have the phosphorus in all steel 
products as low as possible. It is a very poor steel that contains 0.10% 



INGREDIENTS OF AND MATERIALS USED IN STEEL 79 

of phosphorus. The ordinary grades contain as much as 0.08%, and the 
high-grade steels should have less than 0.04%, while in the very best 
steels it should be even lower than this. In fact, this has been reduced 
to below 0.01% in some of the electric furnace steels, and occasionally 
a mere trace is all that is left in the finished product. 

Phosphorus gets into the metal by entering the blast furnace with the 
ores in the form of metallic phosphates, — the form in which it is usually 
found in nature, — and mainly as phosphate of lime, which is a natural 
mineral named apatite. Many metallic oxides unite with it to form 
salts, especially iron and magnesium oxides and lime, but in the presence 
of silica, which is a stronger acid, it is driven away from the slags and 
returned to the iron until the silica has been satisfied. 

In steel, phosphorus has a tendency to cause coarse crystals to form, 
and this tendency is increased with each percentage of carbon. It also 
forms the phosphide, FesP, and this forms a series of alloys with iron. 
The eutectic of this series contains 64% of this phosphide, which equals 
10.24% of phosphorus. A certain percentage of phosphorus will dissolve 
in pure iron and no eutectic will form to produce brittleness, but when 
carbon is added, each increase in percentage exerts an influence on the 
phosphorus that causes it to precipitate from the solid ferrite solution 
and take the eutectic form. Therefore the more pure the iron and the 
less cementite that is in the steel the greater will be the decrease in brittle- 
ness that is caused by phosphorus, while each increase in the percentage 
of carbon increases the tendency of the eutectic to form and the steel 
to assume a coarser crystallization, and this makes it both weaker and 
more brittle. 

Phosphorus is removed from steel to a different degree by the different 
processes of manufacturers. Thus Bessemer steel contains the highest 
percentage of phosphorus, while the other steels contain gradually decreas- 
ing percentages in the order in which they are named: acid open-hearth; 
basic open-hearth; crucible; electric. The acid open-hearth furnace 
requires ores low in phosphorus, while in the basic it is removed by adding 
a sufficient amount of lime to the slag, and in the crucible and electric 
furnaces it is removed by using the proper flux. 

One of the latest methods consists of using an oxidizing slag in such 
a way that it will combine with the phosphorus and form a phosphate, 
and then adding a reducing material to the slag that will convert this 
phosphate into a phosphide. The reducing material is usually ground 
coke that floats on top of the slag and reduces the phosphate without 
interfering with the molten metal below. Owing to the strong com- 
bination of the phosphide, the phosphorus cannot be separated out by 
the iron, without first being changed back to phosphate, and this is impos- 
sible in a reducing atmosphere. 



80 COMPOSITION AND HEAT-TREATMENT OF STEEL 

One charge that was dephosphorized in the Heroult electric furnace 
was taken from a Bessemer converter and analyzed: phosphorus, 0.10%, 
sulphur, 0.16%, manganese, 0.10%, carbon, 0.07%, and silicon, traces. 
When a 15-ton charge of this was put in the furnace a black slag composed 
of 400 pounds each of mill scale and lime was added. This made an 
oxidizing slag that became fluid when the molten metal below was thor- 
oughly oxidized and all the phosphorus had passed into the slag as phos- 
phate of lime (CaO). Ground coke was then added to the top of the 
slag, and this reduced the phosphates therein to calciimi phosphide 
(P2Ca3). Without removing the slag the required amount of carbon, 
silicon, manganese, etc., were added. That there was no return of phos- 
phorus to the steel is shown by the analysis of the final product, which 
was, phosphorus 0.005%, sulphur, 0.005%, with the carbon ranging from 
0.05 to 1.50%, and the manganese and silicon as desired. 

A high phosphorus steel is sometimes used for the third rail in an 
electric railway, as phosphorus will increase hardness without decreasing 
electric conductivity as other ingredients would, and it also decreases 
the purity of the iron less than any other material. This gives the rails 
the necessary hardness and purity to withstand the abrasive wear caused 
by the contact shoes, as well as giving them the necessary conductivity. 

Phosphorus reduces the melting point, makes the metal more fluid, 
and prolongs the period of solidification of all of the iron products. This 
is made useful in such work as art castings, where a detail of figure is of 
more importance than strength, as the metal fills every minute crevice 
in the molds. By keeping the metal in a pasty state for a long time, or 
retarding solidification, the phosphorus allows the graphite to be expelled 
from the solid solution and occupy spaces between the particles of iron. 
This action causes the metal to expand and press into every tiny cavity 
in the mold, and the higher the percentage of phosphorus the longer will 
the solidification be delayed. Certain chemical conditions caused by 
too much phosphorus, too little silicon, etc., might overcome this by 
exerting a tendency to keep the carbon in the combined form. A decreased 
shrinkage because of this expansion may also be caused when the phos- 
phorus separates from its solution in the ferrite and forms a eutectic. 
Phosphorus also increases the tendency toward segregation. 

SULPHUR 

Sulphur is one of the native elements of the earth that is found in 
large quantities free from combinations, especially in volcanic regions, 
as well as combined with metals in the form of sulphide. It is given off 
from the fuels used in reducing the iron ores and refining steel, and in 
the higher temperatures it combines with the oxygen of the air in the 



INGREDIENTS OF AND MATERIALS USED IN STEEL 81 

form of a dioxide, SO2. Part of this is liable to be trapped in the metal 
unless precautions are taken or slags used to remove the sulphur. 

When in steel in the form of sulphide, it causes the metal to crack, 
tear, and check in rolling, forging, heat treating, or hot working, and, 
therefore, the term of "hot-shortness" has been applied to its effect 
on steel. This is the opposite of the effect of phosphorus. Its effect on 
the properties of steel when cold have not been accurately determined, 
but it seems certain that the effect is not detrimental to any extent. 

When steel is heated beyond a dull red, sulphur in the sulphide form 
is said to cause a crystallization to take place, and when high temper- 
atures are reached the grain becomes very coarse, as the sulphur is dis- 
sociated and forms into a gas that diffuses between the iron crystals, 
thus separating them and preventing perfect cohesion. When contrac- 
tion by cooling takes place this may cause microscopic cracks, or even 
cracks large enough to be seen by the naked eye. These, of course, weaken 
the metal. Sulphur and phosphorus increase the tendency toward segre- 
gation. 

Sulphur takes two forms in steel, one of which is sulphide of iron, 
and the other sulphide of manganese. Iron sulphide (FeS) usuallj^ forms 
when the sulphur is high and the nianganese low, as sulphur has a greater 
affinity for manganese than for iron. Until the manganese is satisfied, 
sulphide of iron is not liable to occur, and this latter form does not often 
occur in commercial steels. It is more brittle than manganese sulphide, 
and at the proper temperatures for rolling steels is in a liquid state, thus 
there is no cohesion between it and the molecules of steel. Instead of 
coming together in drops, as manganese sulphide does, it spreads out in 
webs or sheets, which are very pale in color and usually completely sur- 
round the manganese sulphide. When the metal is rolled these are made 
to cover a comparatively large area, and the effect of iron sulphide is 
thus very injurious to steel, as it is very weak and liable to break along 
these webs or sheets. 0-^dng to its liquid state iron sulphide is more 
liable to cause trouble at the rolling temperatures, whether this temper- 
ature be used for rolling or when forging, welding, or heat-treating the 
steel. 

Sulphide of manganese (MnS) is formed by the uniting of manganese 
and sulphur, and is invariably found in steel; this being the form that 
sulphur takes in all the good grades of steel, and if there is enough man- 
ganese present all of the sulphur in the metal will assume this form. It 
usually forms in globular spots, but when the metal is rolled or hammered, 
these generally elongate and under the microscope they show a pale slate 
or dove gray color. 

Opinion differs as to the injurious effect of manganese sulphide upon 
steel, but, however this may be, it is not as injurious as iron sulphide. 



82 COMPOSITION AND HEAT-TREATMENT OF STEEL 

It has been melted in coke-fired assay furnaces that would not melt mild 
steel, which would indicate that it was injurious when steel was heated 
to comparatively high temperatures. It frequently occurs with man- 
ganese silicate (slag) and it segregates together with phosphide of iron 
in the form of ghosts. In this case it may be very injurious to steel, 
and especially so where the sulphide is magnified by rolling the metal. 

Sulphur, when added to soft iron that is low in sulphur, increases the 
strength of the metal, partly by closing the grain and partly by increasing 
the combined carbon. Owing to this tendency to increase the combined 
carbon and form an iron carbide, it has a hardening effect on the metal. 
Its effect on the tensile strength of steel has not been definitely settled, 
but up to 0.10% it does not alter the elastic ratio, elongation, or reduction 
of area to any extent. The actual percentage of sulphur at which steel 
ceases to be malleable or weldable varies Avith other ingredients. Each 
increment of manganese raises it, and it is lowered if the steel ingots are 
cast too hot. 

Attention is being turned to the effect of sulphur, noted in the pre- 
ceding paragraph, and the old theory that sulphur should be reduced to 
a mere trace in steel is beginning to be doubted, as some of these effects 
could be made beneficial if the injurious effects could be overcome. Some 
recent investigations have led to the belief that the oxides are the real 
source of weakness and failures in steel, and if these can be removed, 
the injurious effects of sulphur can at least be nullified, with the probability 
of its being made beneficial. 

According to the old theory, 0.08% of sulphur made crucible steel 
absolutely worthless for welding, forging, rolling, etc., but I have recently 
seen samples of crucible steel that had the oxides reduced to a mininmm, 
and the sulphur at 0.08%, that were forged under the steam hammer 
without any signs of checks. A piece, of this same steel which con- 
tained 0.60% of carbon was welded onto machinery steel to form the 
cutting edge of an axe, and apparently the weld was perfect, as there was 
no signs of a crack when it was ground to shape. This axe was stood 
on an anvil with the cutting edge up, and given 20 blows with a heavy 
sledge before the edge broke, and even then the weld was not harmed. 

Another test was to drift a hole 4 inches in diameter in stock 1^ inches 
thick and 4 inches wide without destroying the drift. In still another 
test a f-inch set stood 200 blows from a 12-pound sledge without breaking. 
This same set was then used in the daily work at the mill until it was 
worn out, and it outlasted two sets made from stock steel. The tensile 
strength was a little better than the ordinary in this high sulphur steel. 

The sulphur content was carried still higher in later tests and it was 
found that with sulphur up to 0.13 per cent, no injurious effects were 
apparent in the steel and the metal did not develop the "hot -shortness'* 



INGREDIENTS OF AND MATERIALS USED IN STEEL 83 

that every one heretofore has attributed to the effect that sulphur has 
upon steel. Above a sulphur content of 0. 13% the metal began to show- 
signs of brittleness and was clearly injurious to the steel. 

With steels as ordinarily made at present the sulphur should not exceed 
0.10% for any use, but for tool making or other uses where the metal has 
to be repeatedly heated and cooled this should not be over 0.03%, and 
preferably as much lower as possible. Steel as now made would be much 
better for nearly all kinds of work if the sulphur could be reduced to a 
trace. 

OXYGEN, HYDKOGEN, AND NITEOGEN 

Of all the elements that enter into the composition of the earth's 
crust, oxygen forms nearly one-half, or, to be more explicit, 47.29%. 
At the higher temperatures it has a greater or lesser affinity for and 
unites with every other elemental substance known, except fluorine, 
helium, neon, argon, krypton, and xenos, and it acts readily upon a large 
number of compounds. At the ordinary temperatures oxygen does not 
act readily upon most other things. Its simple compounds are called 
oxides, and these form with the production of heat. One of the elements 
that combine with it at low temperatures is iron, and this is coated with 
an oxide when heated to about 400° F., or at nearly any temperature in 
the presence of moisture. Iron does not occur in nature except in com- 
bination with oxygen, and occasionally other elements are found com- 
bined with these. 

Hydrogen is the lightest substance known, and like oxygen is a gas 
that is colorless, tasteless, and odorless. It has a high chemical affinity 
for oxygen, and is a good reducing agent that acts by taking the oxygen 
away from substances. It has a great affinity for carbon, and forms 
something like 200 combinations of hydrocarbon. When iron is heated 
to a red heat it easily penetrates this and forms into a compound. 

Nitrogen, owing to its inactivity, serves principally as a dilutent of 
oxygen. 

These three gases readily dissolve in iron or steel when it is molten, 
but as it solidifies comes out of the state of solution, and then much the 
larger part passes away. A portion, however, is usually entrapped, and 
this portion if segregated in large bodies causes blow-holes, gas bubbles, 
etc. Carbon monoxide gas (CO), which may be generated during the 
solidification period by a reaction of the oxide of iron with the carbon 
when carburizing, is also a cause of blow-holes. These blow-holes are 
usually removed by the use of the deoxidizers, such as manganese, silicon, 
aluminum, etc. Another portion of these gases, however, is liable to 
form microscopic bubbles that are difficult to remove from the metal, 
and consequently they form the occluded gases and oxides that are just 



84 COMPOSITION AND HEAT-TREATMENT OF STEEL 

beginning to be recognized as among the most harmful things in steel; 
oxygen probably being the most weakening element that can be left in 
steel, with hydrogen and nitrogen closely following. 

As evidence of this, Bessemer steel, which is purified by blowing air 
through it, is the poorest and weakest of steels; while open-hearth steel, 
which is purified without this blast of air, but is not protected from the 
air striking the surface of the bath, comes next; and crucible steel being 
protected from air by the melting process taking place in a closed pot, 
is the strongest and finest grained of all the steels, except those made 
in the electric furnace, and this is also protected from the air. Another 
proof is the added static and dynamic properties, wearing qualities, etc., 
that are given to steels, by such elements as vanadium, titanium, etc., 
when they are used to cleanse the metal of these gases. 

Oxide occurs in very small black specks throughout the metal and 
can only be seen when the surface has been perfectly polished and mag- 
nified at least one thousand times. They are invariably found in steels 
that produce blisters when pickling, and this leads to the conclusion that 
the blisters were formed by the reduction of oxide by the nascent hydro- 
gen evolved during the pickling process. High-carbon steel rods that con- 
tain the same impurity occasionally fracture in the pickling bath and 
doubtless the same pressure that blows a blister in mild steel will cause 
a rupture in hard steel. 

Owing to the gaseous nature of oxygen, and the fact that the drillings 
must be very fine, it is difficult to analyze steel for the oxygen content. 
A series of tests, however, was carried out by E. F. Law, of London, by 
cutting a piece from each of eleven bars of acid and basic Bessemer steel 
that contained from 0.10 to 0.18% of carbon, and only a trace of silicon. 
Each piece was then rolled into 24 sheets which were pickled and annealed 
by the usual process. An adjacent piece of the bar was analyzed, exam- 
ined with a microscope, and the oxygen determined. The result of these 
tests was as follows: (See table on page 85.) 

An examination of the table will show that as the oxygen content 
increased the number of blistered sheets increased, while the percentage 
of sulphur seemed to have no effect on the blistering; the set containing 
19 blistered sheets only showing 0.071% of sulphur, while the set of sheets 
that did not blister at all contained 0.076, 0.069, and 0.061% of sulphur, 
respectively. By way of comparison a piece of basic Bessemer steel 
was analyzed just before the ferro-manganese was added, and this showed 
0.062% of oxygen. The results shown here seem to forcibly confirm the 
oxide theory. 

It might appear at first sight that the quantities present are extremely 
small, but in making comparisons we should not consider alone the amount 
of the elements present, but also the combinations of these elements that 



INGREDIENTS OF AND MATERIALS USED IN STEEL 85 

Table Showing Effect of Oxygen on Blistering 



Kind of 

Bessemer 

Steel 


Analysis 


Microscopical 
Appearance 


Sheets in 24 

that 

Blistered 


Percentages 

of 

Oxygen 


S 


P 


Mn 


Acid 

Basic 

Acid 

Basic 

Basic 

Acid 

Basic 

Basic 

Acid 

Basic 

Basic 


.061 
.069 
.076 
.101 
.080 
.106 
.079 
.045 
.061 
.080 
.071 


.049 
.034 
.070 
.126 
.066 
.188 
.098 
.075 
.081 
.068 
.090 


.340 
.385 
.350 
.475 
.430 
.320 
.440 
.473 
.350 
.450 
480 


Very good 

Good 

Good 

Fair 
Moderate 

Bad 

Bad 

Bad 

Bad 

Bad 
Very bad 





4 
6 
7 
7 
8 
9 
12 
19 


.021 

.021 
.022 
.025 
.026 
.026 
.027 
.034 
.032 
.030 
.046 



influence the quality of the steel. Thus, we speak of 0.05% of sulphur, 
when in reality it is 0.13% of manganese sulphide that affects the quality 
of the steel. Oxygen has only half the atomic weight of sulphur, and 
is capable of forming larger quantities of compounds, therefore it exerts a 
greater influence. Thus, where 0.05% of sulphur corresponds to 0.13% of 
manganese sulphide, 0.05% of oxygen corresponds to 0.22% of ferrous acid. 

Another fact brought out in these tests is that the amoimt of oxide 
visible under the microscope was much less than would be expected from 
the amount actually found by chemical analysis, and this might be 
accounted for by the fact that a considerable quantity of oxide was in 
solution in the steel surrounding the black oxide spots. The oxide show- 
ing on the surface of a polished piece was also reduced by the aid of hydro- 
gen and an electric current, and the pits thus formed occupied a much 
larger area than the spots of oxide seen by the microscope. 

Steels containing oxides also apparently rust much quicker than those 
free from them, and with two pieces placed side by side the oxide steel 
will show rusting long before the other, while in dilute acid solutions 
steels containing oxides corrode more easily and much faster than those 
free from oxides. This has led to the production of a metal called "Ingot 
iron," in which the total impurities, except carl:)on, have been reduced 
to from 0.05 to 0.08% and the carbon content to 0.02%. A typical anal- 
ysis showed carbon 0.02%; manganese, 0.01%; sulphur, 0.02%; oxygen, 
0.03%, and phosphorus and silicon a trace. 

In the making of this metal the theory that ferro-manganese was needed 
to produce a workable metal in the hot condition was doubted, and the 
usual ferro-manganese decarburizer was omitted. Open-hearth furnaces 
are worked entirely on cold pig iron low in silicon and sulphur, and with 



86 COMPOSITION AND HEAT-TREATMENT OF STEEL 

the phosphorus Hmited to the content for Bessemer working. An active 
basic slag is maintained that is composed of limestone and fluorspar, with 
a comparatively large amount of the latter flux to prevent the phosphorus 
from returning to the metal at the high temperature of 3000° to 3100° F., 
that is maintained toward the end of the process. A fairly large propor- 
tion of scrap is charged in the form of open-hearth mill scrap and low- 
carbon steel turnings, the larger part being of the latter. When sufficient 
mill scale can be obtained it is substituted for ore in the charge. 

The removal of oxygen, probably in the metal in the form of oxides, 
is the most important, and instead of manganese, ferro-silicon, or an equiv- 
alent material, is added to the bath to remove the oxides, and the other 
gases are removed by adding below 0.10% of granular aluminum in the 
ladle. The time consumed for each charge is about 10 hours, and the 
boiling is carried to a high temperature to thoroughly oxidize the impuri- 
ties. This brings the temperature very high in the final stages, owing 
to the higher melting point of the purer materials. When the oxygen 
is not removed the metal is red-short and cracks on the edges when 
rolling, but this can be removed by various substances, such as pig iron, 
silicon, vanadium, titanium, aluminum, etc. 

COPPER 

Copper is a widely distributed element of the earth's crust, that occurs 
in large quantities; sometimes in the uncombined condition, such as the 
native copper of the Lake Superior regions. It is very malleable and 
tenacious. In most of the copper ores used, sulphur and iron occurs, and 
in most of the iron ores, used for making steel, copper occurs. Some con- 
tain as high as 1% of copper, and many of the Bessemer and open-hearth 
steels contain from 0.30 to 0.50% of this metal. That copper associates 
with all steels in perfect unison and does not segregate until above 4% 
has been added is a well-established fact. 

Copper can be alloyed in all proportions, with iron containing 0.15% 
of carbon, and with 0.09% of sulphur added to this, no segregation will 
occur until 7.70% of copper has been added. With the sulphur low and 
the carbon at 0.20% no pronounced segregation appears until a copper 
content of 40% is reached, while with 0.40% of carbon it occurs with 
a copper content of about 30%; with carbon, 0.60% at 20% copper; 
with carbon, 0.80% at 12% copper, and with the carbon at 1% copper 
segregation is liable to occur when the copper is 8%. This, however, is 
only a general rule, and it can be varied greatly with various other ingre- 
dients and methods of making the steel. As the best results seem to 
be obtained when copper is kept below 5%, segregation will not be much 
of a factor in copper steel. 



INGREDIENTS OF AND MATERIALS USED IN STEEL 87 

Hard and soft steels with a percentage of copper as one of the ingre- 
dients have been used for many purposes with the usual number of fail- 
ures, but these failures have always been traced to other ingredients 
and none to the copper contents. Crank-shafts for the United States' 
battleships and gun tubes for 6-inch guns, have been made out of steel 
containing 0.57% copper, and they stood successfully all of the tests 
required l^y the Government. 

Coiimiercially steels containing over 4% of copper cannot be rolled 
and forged unless the percentage of carbon is very low, owing to its hard- 
ening effect and the consequent brittleness it gives to the metal. With 
percentages up to 4, the copper all goes into solution in the iron, but 
above that, saturation begins to occur. The point at which saturation 
begins appears to be between 4 and 8%; it being lowered as the carbon 
content is increased. When the copper content is increased to above 
8% free copper occurs; in a fibrous form in the soft or semi-soft steels, 
and in nodules in the higher carbon steel. 

When there is enough sulphur in the steel, it will form with the copper 
a copper sulphide, according to the formula (CujS), but if there is an excess 
of copper it will combine with the iron. Steels containing copper and 
copper sulphide have an irregular structure, as regards the size and join- 
ing together of the ferrite crj'stals, as these imbricate with one another 
with curved junctions. This gives the metal a higher strength than that 
of steel without copper. 

Copper and copper-sulphide principally distribute themselves between 
the crystals of ferrite, which they envelope and prevent the red-short- 
ness that it is claimed is caused by sulphur. They also cause the quantity 
of pearlite to increase and the grains of this to assume a finer structure 
and permeate the metal more and more with each increase in copper. 
In fact, the structure so closely approaches the martensitic form that 
it has been mistaken for this in some instances, and in a 7% copper steel 
threads of cementite and of pearlite appeared. In this way they inten- 
sify the iron carbide and give to the metal a greater hardness as well 
as enable it to be hardened more easily when heating and quenching. 
Copper also lowers the recalescent point from 100 to 150° F. below that 
of ordinary steels, but it never brings this below 800° F. In this it about 
equals high-carbon steel. The 1 to 5% copper steels that are liable to 
become commercially successful should be quenched in water from about 
1325° F. or in oil. 

It is possible to find traces of copper sulphide in metal that contains 
only 7% of iron and 0.025% of sulphur. As a small amount of iron in 
solution in copper makes copper harder, this might suggest the idea of 
strengthening copper or copper alloys with iron. 

Copper increases the hardness of steel, as the copper content increases. 



88 COMPOSITION AND HEAT-TREATMENT OF STEEL 

When the carbon content is low it has a greater effect than when it is 
high ; in some cases ahnost doubhng the Brinnell hardness, and it reached 
its maximum increase in one series of tests at from 10 to 15% copper. 
It does not give any color to steel until 8% has been passed. 

With the carbon content high, copper steel is difficult to work mechan- 
ically, but it can be easily cast into the shapes desired. If, however, the 
carbon is kept below 0.50%, steels containing as high as 4% of copper 
can be easily and successfully rolled and forged, and the heat treatment 
made a less delicate operation. Such steels seem to have a future as they 
have a greater tensile strength and elastic limits than the same steel 
without copper; a better elongation and contraction; more resiliency; 
a greater resistance to shock and torsional strains; a greater hardness 
without loss of ductility and a finer grain. The copper steels closely 
resemble nickel or chromium steel, and follow the same laws as to their 
increases of strength for each increase of percentage, but they possess a 
higher elastic limit and maximum strength than nickel steel as well as 
greater dynamic strengths. Copper has a more active influence on steel 
than nickel or manganese and, nearly approximating chromium, molyb- 
denum, and vanadium, and it is a cheaper alloying material than these. 

Copper steels as rolled show greater tensile strength with each increase 
of copper, and this is more manifest with the lower carbon percentages, 
but it is not dependable in this state. Annealing corrects this to a large 
extent, but does not leave the metal much if any stronger than the ordi- 
nary steel. Hardening and tempering after this, however, more than 
doubles the tensile strength and elastic limit, and brings the latter up 
close to the former with a good percentage of contraction. This would 
indicate that if copper steels were well made they would be able to with- 
stand shock, torsional, alternating, or vibrational strains, as well as the 
high-grade steels of the present day, and, owing to the comparative cheap- 
ness of copper, it could be produced cheaper. 

Some corrosion tests were carried on that showed that corrosion was 
lower by something like 100% in copper steel than in steels that contained 
no copper. The electrical resistant is also increased in steels containing 
copper, and reaches its maximum in a 0.15% carbon steel at 2% of copper; 
in a 0.7% carbon steel at 0.5% copper, and in a 1.7% carbon steel at 
0.35% copper. 

In refining the steel, the carbon, silicon, and phosphorus seem to remain 
fairly constant, with a large excess of metallic oxide, while aluminum and 
manganese pass into the slag with only a slight excess of oxygen. 

ARSENIC AND ANALOGOUS ELEMENTS ANTIMONY AND BISMUTH 

Phosphorus, arsenic, antimony, and bismuth all belong to the same 
chemical group, and in general form compounds of the same character 



INGREDIENTS OF AND MATERIALS USED IN STEEL 89 

and of similar composition. Like nitrogen they unite with metals to 
form binary compounds, called phosphides, arsenides, and antimonides. 
They all form two oxides, which contain 2 atoms of the above-named 
elements to 3 atoms and 5 atoms of oxygen. Of these elements phos- 
phorus occurs most abundantly in nature: arsenic and antimony next, 
and bismuth last. The last three occur sometimes in the uncombined 
state, but phosphorus always occurs in combination with other elem.ents. 

Many steels contain an appreciable percentage of arsenic, as it com- 
pounds with iron in forms that are similar to the sulphide which it fre- 
quently accompanies. The arsenides, which are its compounds with 
metals, occur very widely distributed, and often accompany the sulphides 
which they are similar to. The most common compound of this kind has 
the composition FeAsS, and may, therefore, be regarded as iron pyrites 
(FeSj), in which one atom of arsenic has been substituted for one atom 
of sulphur. Simple compounds of pyrite and arsenic occur that are anal- 
ogous to the sulphide FeS2, and combinations of sulphur and arsenic 
form into sulphides. 

When steel contains an appreciable percentage of arsenic it will give 
off an odor similar to garlic when heated to a red heat, and this odoi- may 
become very intense at a welding or forging heat. As an element it is 
not poisonous, but when oxidized it may become extremely so and it 
is easily oxicUzed. 

If the arsenic in commercial steel does not exceed 0.20% it does not 
have any material effect upon the mechanical property, as the elongation 
and reduction of area are not changed and the tenacity is but slightly 
increased. This leaves the bending properties unchanged at ordinary 
temperature. Above 0.20% the strength of steel is increased and the 
toughness decreased with each increase in the percentage of arsenic until 
4% is reached, when the elongation and reduction of area become nil 
and the steel becomes very brittle. Even with 4%, however, it does not 
affect the hot working of the metal, and it can be alloyed with iron in 
proportions as high as 56% under certain conditions of mixing. These 
conditions, however, are difficult to fulfil. 

By ordinary methods attempts have been made to produce alloys 
in various proportions up to 10%, of arsenic, but when analj'zed the sample 
showed that the maximum of arsenic taken up and retained by the iron 
was about 4%, this appearing to be about the largest amount that could 
be commercially added to steel. While steels with the higher percentage 
of arsenic are brittle, no special difficulty is met with in machining them 
with any percentage of arsenic. 

Owing to the fact that arsenic, -when present in acid pickling solutions, 
causes a marked reduction in the rate of attack by the acid, it was thought 
that if the arsenic was added to the iron it might resist the attacks of 



90 COMPOSITION AND HEAT-TREATMENT OF STEEL 

corrosion and become more durable. Numerous tests that were made, 
however, show no appreciable difference in the non-corrosive qualities 
of iron and steel that contained arsenic and those of the ordinary brand. 

The benefits to be derived from alloyed arsenic with iron or steel 
seems to be in regard to their magnetic property, as some very interesting 
results have been obtained. Arsenic with a temperature of sublimation 
of 850° F. alloys with iron, even though it has passed this temperature 
long before the fusion of the iron begins, practically in the proportions of 
the solid mixtures up to an arsenic content of 1%. With each increase 
of arsenic in steel up to 5%, the magnetic qualities of iron are made better 
and the arsenic alloys are on an equality with the best electrolytic material 
known for magnetizing forces. When the metal is heated to 1250? F. 
and slowly cooled, so as to allow the grain to become normal and the 
forging or rolling strains to be removed, the metal shows a decided improve- 
ment. A second heating to 1800° F., with slow cooling, improves the 
quality in the lower ranges of the magnetic forces, but there is a falling 
off in the upper ranges of the curve. Quenching from 1650° F. shows 
no hardening and but slight changes in the magnetization curves. Arsenic 
added to iron imparts to the alloy magnetic qualities excelling those of 
the purest iron, and at least equaling those of the best material from 
which data is obtainable. 

Antimony may be added to iron in quite large percentages, but above 
a content of 1% the metal is not forgeable, and only then with difficulty. 
It renders the metal brittle so that it is practically Avorthless, and it is 
of a lower grade magnetically than the ordinary electrolytic iron. Thus 
while antimony is in the same chemical group as arsenic, it makes iron 
products that are difficult to work and have no apparent value as a mag- 
netic material. Antimony is iiseful in the non-ferrous alloys for the 
hardening effect it gives, and that it expands when solidifying makes it 
valuable for such uses as type casting. These same properties make 
it detrimental to iron and steel products, and luckily it does not appear 
in the crude materials used for making these. 

Bismuth, like antimony, does not occur in combination with iron or 
in the products used for producing the iron ore when refining it into steel, 
conseqently it does not have to be removed as an impurity. To a greater 
degree than antimony it has the property of expansion when passing from 
the liquid to the solid state, and therefore it is useful in non-ferrous 
alloys. 

When 2% of bismuth, the most diamagnetic element known, was 
added to iron, it improved the already high magnetic quality of the pure 
iron. The density values reached exceed those obtained from any of 
several hundred other different alloys that have been tested. How much 
bismuth remained in the metal after adding the 2%, however, was not 



INGREDIENTS OF AND MATERIALS USED IN STEEL 91 

known. With bismuth alloys there is but little increase of resistance. 
Arsenic and antimony, however, give a decided increase of resistance to 
iron, and in some cases this was from 62 to 67%. 

BORON 

In nature boron chiefly occurs in the form of boric acid, or as salts 
of this acid, such as borax, a sodium salt, or two calcium salts. It belongs 
to the same chemical family as aluminum, and is very similar to it in 
the composition of its compounds, but its oxide is acidic, while the oxide 
of aluminum is basic. In some respects it resembles the members of the 
family to which nitrogen and phosphorus belong, but it belongs to a dif- 
ferent family. It has a strong affinity for nitrogen, especially at the 
higher temperatures, and also combines readily with sulphur and chlorine. 
Some of the boron crystals contain carbon and aluminum, which seem 
to be in combination with the boron. 

Ferro-boron can be prepared from borate of lime, in the electric fur- 
nace, without any special difficulty, and the above data would suggest 
that boron might have some qualities that would be beneficial to steel, 
but very little in the way of investigations has so far been done. What 
little has been done would indicate that boron acts like carbon in many 
respects, notable among which is that of adding hardness to the metal. 

In some recent tests that were made on steel containing 0.20% of 
carbon and 0.20, 0.50, 0.80, 1, and 2% of boron, the Brinell hardness of 
the samples tested and quenched at 1460° F., was three times that of the 
annealed pieces, and equal to that of carbon steel similarly treated. Not- 
withstanding this the hardened samples could be easily filed, sawed, or 
machined, while 0.37% carbon steel, similarly treated, could not be 
scratched except with an emery wheeel. 

This is adding evidence to the statement that has been made several 
times, but disputed by some, namely: that hardness has no relation tO' 
the ease or difficulty with which steel can be machined "wath cutting tools. 
The tests also show that boron confers upon steel the property of temper- 
ing; but a tempering that is very different from that conferred upon the 
metal by carbon, in that it increases the tensile strength and elastic limit, 
without materially increasing the toughness or hardness to machine. 
On the other hand, the ability to withstand shock tests was doubled by 
quenching, and the elastic limit was brought up close to the tensile strength. 

In heating boron steels they show a definite emission of heat at 2100° 
F., which resembles the recalescent point in high-carbon steel. Slightly 
marked critical points appear at 1900°, 1525°, 1350°, and 1225° F. The 
three latter are about the temperature of the points Ar3, Ar2, and Arl 
of mild steel. The point at 1240° F. is definitely shown in carbonaceous 



92 COMPOSITION AND HEAT-TREATMENT OF STEEL 

iron, but when boron is added and the iron heated, this point almost 
entirely disappears, and is replaced by the point at 2100° F. 

Boron may be said to give steel a hardness that increases its strength, 
up to a content of 2% of boron, providing the carbon is kept below 0.02%, 
but beyond a content of 2% boron or 0.2% carbon, the metal becomes 
so brittle that it is weakened and easily powdered under a hammer. Other 
elements might be found, with further investigations, that would over- 
come this brittleness and make boron more useful for special alloys of steel. 

Microscopical examinations show intense black spots in boron steels 
that are polished and etched, first with picric acid and then with picrate 
of sodium. These increase in quantity with each increase in the per- 
centage of boron. These spots may be a combination of boron-iroii; a 
solid solution of boron-iron that separates out from the former and con- 
tains a percentage of boron that is very low; a borocarbide of iron, or a 
boride of carbon. In specimens thus treated the ferrite appears white, 
the pearlite grayish, and the special constituent very black. 

On annealing, the volume of pearlite increases and the special con- 
stituent disappears by forming a eutectic with the ferrite that at times 
is strongly marked. By annealing in the presence of oxide of iron, so 
as to decarburize the metal, the pearlite is first caused to disappear and 
then the special constituent. 

In carbonizing the special constituent is not increased by case-harden- 
ing, although at the edges a layer of pearlite is found and this is thinner 
if the metal does not contain boron. This would indicate that the pene- 
tration of carbon is delayed by boron, and that the amount of the special 
constituent depends upon the percentage of boron, and is independent of 
the carbon content. 

In the quenched steels, the special constituent was hardly discernible 
when the percentage of boron was below 0.50, but large quantities appeared 
in the steels with the higher percentages of boron. This was not altered 
even when the quenching was carried to 2200° F. The percentage of 
carbon increases the solubility of the special constituent and the higher 
the percentage of boron the less easily does it dissolve. 

The above data would indicate that the black spots were a boro- 
carbide of iron, and its percentage of carbon very low; otherwise a phenom- 
ena would occur similar to that brought out in the investigations of the 
vanadium steels, i.e., as the boron increased the pearlite would diminish; 
but in these steels the special constituent continues to increase. 

Boron steels are very weak and brittle in the normal state, and, if 
heated to a very high temperature, crumble when forged or rolled. But 
if heated to a dull red they can easily be forged, rolled, or otherwise mechan- 
ically worked, as they act much like soft steel. This will make them use- 
less in the raw state, but after quenching they possess a high tensile 



INGREDIENTS OF AND MATERIALS USED IN STEEL 93 

strength, a very high elastic limit, and are not any more brittle than the 
special steels that are in actual use at present. 

Borax is a sodium salt from which amorphous boron, in almost pure 
form, can be obtained by heating the borax with magnesium powder. 
It has been used by many misinformed people as part of a mixture for 
carbonizing steel, or in a special compound for hardening it, but they 
have never given any good reason for its use or shown any results that 
were obtained thereby. It, like boron, retards the penetration of carbon, 
but when used in a quenching bath may aid in producing a greater hard- 
ness, or preventing the metal from cracking or checking. Common table 
salt (NaCl), however, gives much better results, and is easier obtained 
and cheaper. Therefore borax is not useful here, and is harmful in the 
making or treating of steel in other ways. 

TANTALUM 

Tantalum is one of the rare elements that is never found free in nature, 
but is in combination with the minerals columbite and tantalite, accom- 
panied by niobium. In chemistry it is grouped with vanadium, niobium, 
and didymium, all of which are rare. Its rareness, and consequent cost, 
has prohibited it from being experimented with to any extent, but one 
series of tests that was conducted appeared to prove that it had a harden- 
ing effect upon steel, similar to that exerted by tungsten and molybdenum, 
and to a certain extent gave promise of being beneficial for high-speed 
steel tools. 

In all of the eight tests made, the tantalum which varied from 0.42 to 
1.69% increased the tensile strength, elastic limit, elongation, and reduc- 
tion of area over that of the same steel without tantalum, but when nickel 
or chromium was added in place of the tantalum, the same strengths were 
obtained and in one case 1.10% of chromium gave about 10% greater 
strength than 0.43% of tantalum. The greatest increases in strength 
were obtained with the smallest percentages of tantalum. 

Under the microscope a dark constituent appeared that was greater 
in quantity as the percentage of tantalum increased, and this occurred 
in a finely granular matrix that in the hardened specimens seemed to 
be martensitic and more or less homogeneous. 

From the results obtained and its similarity to vanadium the sugges- 
tion occurs that it acts on steel as a scavenger similar to this, and the 
best results would be obtained in the quaternary steels, but no evidence 
has been submitteci to prove that it is any better, or even as good as the 
alloying materials already in use, and which are much cheaper. It is 
also very difficult to separate it from niobium, -with which it is always 
combined, and this element is liable to cause erratic results in steel. 



94 COMPOSITION AND HEAT-TREATMENT OF STEEL 



PLATINUM 

Platinum always occurs in nature with five other elements, more rare 
than itself, that are divided into two chemical sub-groups commonly called 
the platinum metals. These nearly always occur in an alloy in which 
the platinum is from 50 to 80%, and all the other five compose the balance. 

It forms two oxides, and two sulphides. It is very ductile and is a 
grayish-white metal that looks like steel. It can be welded at a white 
heat. A compound of platinum and silicon can be formed by bringing 
it in contact with red-hot charcoal and sihcon dioxide. Nitric, hydro- 
chloric, or sulphuric acid will not dissolve it. Platinum, when finely 
divided, has an extraordinary power of condensing gases upon its surface; 
for instance, it absorbs 200 times its own volume of oxygen, also other 
gases similarly. The oxygen is then in the active condition, and oxidiz- 
able materials are easily oxidized when brought into contact with it. 
Thus when sulphur dioxide and oxygen flow together over spongy plati- 
num, or even the compact metal, they form sulphur trioxide bj- a unity 
of the two gases, or when hydrogen flovN^s against the spongy platinum 
it takes fire. 

Iridium belongs to the same chemical group and, when this is alloyed 
with platinum in the proportions of 1 to 9 respectively, it reduces the 
malleability of platinum, which can be easily draivn into very fine wire; 
makes the alloy harder; more difficult to fuse; as elastic as steel; unchange- 
able in the air, and capable of taking a high polish. 

While platinum is but little cheaper than gold, the above properties 
have led to its being investigated as an alloying material for iron, but 
as yet the experiments have been very few, and limited in their scope. 
Platinum has no transformation points, and it consequently reduces 
those of iron when mixed with it. Up to 10% of platinum, two transforma- 
tion or recalescent points occur, while with the platinum from 10 to 40% 
but one point is produced. The melting-point diagram shows consider- 
able analogy to that of the nickel-iron alloys, but this is stronger when 
the alloys are rich in iron than when they are rich in nickel or platinum. 

The hardness of the platinum alloys decreases from to 5% of platinum, 
and then gradually increases from there to a platinum content of 40%, 
after which it remains fairly constant until 90% of platinum is reached, and 
then reduces. At 50%; of platinum the greatest brittleness occurs. 

From to 90% of platinum all the alloys are magnetic, and this dimin- 
ishes in the same ratio as the iron in percentages of from 80 to 20 of that 
metal. Alloys with the platinum from 10 to 50% lose their magnetic 
power when heated to from 1475° to 1200° F., and it returns at a much 
lower temperature when cooling. Alloys with the platinum from 60 to 
90% regain their magnetic power at a temperature even lower than this. 



INGREDIENTS OF AND MATERIALS USED IN STEEL 95 



NICKEL 

The chemical sub-group in which nickel belongs is composed of iron, 
cobalt, and nickel, and in many respects they are very similar. It occurs 
native in meteorites, and the iron meteorites always contain nickel. The 
principal minerals that contain it are niccolite and gersdorffite. Several 
large deposits of native alloys of nickel and copper have been found, and 
owing to the difficulty of separating it and the value of this combination 
as a non-corrosive alloy, it has been rolled and cast into commercial shapes 
under the name of monel metal. 

Nickel, however, is separated from its impurities for many uses, and 
one of the most important of these is its iise as an alloying material in 
the manufacture of special steels. It is a white metal with a slight yellow 
cast, and is very hard and capable of being highly polished. It is very 
brittle in its ordinary condition, but when, treated with magnesium 
becomes very malleable. 

Nickel reduces the size of the crystalline structure and increases the 
toughness of steel. It brings the elastic limit closer to the tensile strength, 
and microscopic cracks, that are liable to develop into larger cracks and 
produce rupture, do not appear as cpickly in steels containing nickel 
as in those without it. It also makes steel more resilient or springy, 
increases the hardness, raises the tensile strength, and segregates only 
slightly. 

Nickel was first added to steel for the pm-pose of overcoming the 
property of "sudden rupture," which is inherent in all carbon steels. 
This it has done to a large extent, as it makes steel better al)le to with- 
stand severe shock and torsional stresses, as well as compressive stresses; 
but this is not due to hardness as soft steel cannot be made hard by the 
addition of nickel, except in large quantities, as it is considered that 17.55% 
of nickel is the equivalent of only 1% of carbon, that contains the maxi- 
mum amount of hardening carbon. 

The properties of nickel steel depend as much upon the carbon content 
as on the nickel. The fact that a 2 or 3.5% nickel steel is used means 
nothing unless the carbon content is right for the use to which the steel 
is to be put. To illustrate, a steel containing 2% nickel and 0.12% car- 
bon has a good tensile strength with a great elongation, and is useful for 
some purposes, while a steel that is equally useful for another purpose 
may contain 2% nickel and 0.9%, carbon, and this would give it a high 
tensile strength with very little elongation. With a high carbon content 
nickel steel is difficult to harden, especially locally, as fissures and cracks 
tend to develop in quenching. It also has more tendency to warp in 
quenching than other steels and may be decarbonized by heating. These 
tendencies may be overcome to a great extent if the metal is thoroughly 



96 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



annealed before it is machined to size, in order to relieve all of the internal 
strains. Then, when quenched, the piece should be immersed in the bath 
so that the liquid can cover the greatest possible surface at the instant 
it strikes the bath, and it should be agitated while cooling. 




Fig. 47. — Cutting test bars. 

Nickel also gives steel a tendency to show laminations, and make it 
weaker at right angle to, than in line with the direction in which it is 
rolled. The higher the nickel content the greater will be the contrast 
between the strength in these two directions. This is best shown by 



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tests which were made on test bars 1 and 2, cut from a piece of 3.5% 
nickel steel as indicated in Fig. 47. Test bar 1 showed an elongation 
of 12% and a reduction of area of 17%. Test bar 2 gave an elongation 
of 25% and a reduction of area of 65%. The good qualities which nickel 



INGREDIENTS OF AND MATERIALS USED IN STEEL 97 

gives to steel offset these bad qualities to such an extent that it makes a 
much better steel for gears, crank-shafts and pieces which have similar 
work to perform than the ordinary carbon steel. 

The tendency of steel to burn in heat-treating is greatly reduced by 
the addition of nickel, and the extent to which its strength can be swayed 
by heat treatment is remarkable. One series of tests which were made 
showed a tensile strength of 88,000 pounds per square inch, an elastic 
limit of 60,000 pounds per square inch, an elongation of 28% and a reduc- 
tion of area of 58% when in the annealed state. These figures were 
changed by hardening to a tensile strength of 225,000 pounds, an elastic 
limit of 224,500 pounds, an elongation of 8%, and a reduction of area of 
19%. A good quality of carbon steel might show these same figures in 
the annealed state, but they could not be raised to much more than half 
of those found in the nickel steel in its hardened condition. 

Nickel has one peculiarity in its influence on steel which is best shown 
by Fig. 48. Up to 8% it increases the tensile strength and elastic limit; 
from 8 to 15% it produces a steel so brittle that no mechanical tests are 
possible as the metal can be powdered with a hand hammer; at 15% 
the strengths are again restored, and they gradually reduce from that 
point on; from 20 to 25% the elongation rapidly increases, and from 
there on to 50% a gradual increase is shown. 

Steel with percentages of nickel from 30 to 35 give good results for 
valves on internal-combustion engines, as the nickel makes the steel wear 
better and it is not as good a conductor of heat as other metals. Nickel 
steel can be purchased in the open market in nearly all percentages of 
nickel from 1 up to 35%,, and with varying percentages of carbon. 

In Fig. 49 is shown the actual results that were obtained from a series 
of twenty tests, in which the nickel varied from to 20%, and the other 
ingredients remained fairly constant. Ten of the tests were with forged 
steel and ten with cast steel. They give a good idea of the strengths that 
can be expected in nickel steels, although, as has been said many times, 
nickel steel in the annealed or natui'al state is but little better than carbon 
steel, but if properly heat-treated it can be made to double carbon steel 
for static and dynamic strengths, wearing qualities, etc. 

COBALT 

The principal minerals containing cobalt are smaltite and cobaltite, 
and in each of these iron and nickel take the place of a part of the cobalt. 
It, like nickel, forms compounds that are analogous to ferrous compounds, 
and also a few that are analogous to ferric compounds. In the latter 
case, its power is greater than that of nickel. Cobalt is harder than iron, 
melts at a slightly lower temperature, and has a silver-white color with 
a tinge of red. 



98 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



In the matter of cobalt-iron alloys, investigations up to a cobalt per- 
centage of 60 have been made. The mechanical properties were but 
little modified in these, but the breaking strength and the elastic limit 
cross slowly, while the elongation and the reduction in cross-section are 



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inversely modified. Notwithstanding its similarity to nickel the cobalt 
steels so far examined have no industrial interest and do not present any 
of the qualities of the nickel steels. 

In general, cobalt in steels enters into solution in the iron, and the 
carbon exists therein — at least in the range of the experiments made 



INGREDIENTS OF AND MATERIALS USED IN STEEL 99 

— in the shape of iron carbide. The mechanical properties of these steels 
do not seem to promise any industrial application thereof: but they show 
very clearly the marked difference between tin, titanium, and silicium 
steels on the one hand, and nickel and cobalt steels on the other. 

CHROMIUM 

Chromium, tungsten, molybdenum, and uranium are in the same 
chemical group, and all show some resemblance to the elements in the 
sulphur group. Each form an oxide, and when they lose their oxygen 
form compounds with little or no acid character. 

Chromium forms three series of compounds, and it occurs in nature 
principally in the mineral chromite, which is commonly called chrome 
iron ore, or chromic iron, with the composition FeCr204. It is very hard, 
and can be highly polished; has a bright metallic luster, and is difficult 
to fuse, its melting point being above that of platinum. In steel making 
it is used as a ferro-chromium, containing 60% chromium and 40% iron. 
Owing to its high melting temperature, this has to be made in an electric 
furnace from chrome iron ore. 

Chromium gives to steel a mineral hardness, and refines the grain 
remarkably, owing to its tendency to prevent the development of the crys- 
talline structure; but it gives no self-hardening properties, although it 
is the element used in combination with tungsten that produces the quality 
of "red-hardness" in high-speed steels. 

Chromium added to steel in percentages up to 5 increases the ten- 
sile strength and elastic limit of hardened steel. In the annealed state 
the tensile strength is raised until 6.5%. is reached and the elastic limit 
is raised up to 3%, and this does not lower to any great extent until 9% 
is reached. After these percentages are passed a decided reduction takes 
place. This is best shown in Fig. 50. 

Extreme hardness jnay be obtained in chromium steels as the chromium 
intensifies the sensitiveness of the metal to quenching, and greatly reduces 
the liability of fracture that is found in carbon steels. This is due to 
the chromium making the critical changes of steel take place much more 
slowly. Chromium steel practically shows no grain or fiber and possesses 
a high power of resistance to shocks. This has made it almost universally 
used for armor plate. 

With 2% of chromium, steel is very difficult to cut cold, and is quite 
brittle; with higher percentages than this it is impossible to finish it with 
machine tools except by grinding. When chromium is combined with 
nickel or vanadium, it makes the strongest, toughest, and best wearing 
steel on the market, and it can be machined and forged much more easily 
than when chromium alone is used. Small gears can be made with these 
alloying materials added to steel, that if properly heat-treated will be 



100 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



so tough and strong as to make it almost impossible to bieak out a tooth, 
even with a sledge hanmier. 

Some of the best grades of chrome-nickel or chrome-vanadium steel 
contain from 0.75 to 1.50% of chromium. If more than this is used the 
metal is too brittle and it is difficult to preserve the high strengths which 
are given by the lower percentages. The carbon content is also kept 
comparatively low, as a percentage of 0.45 of carbon makes the metal 
about as hard as can be cut with machine tools, even when thoroughly 
annealed. Many of these steels contain only 0.25% of carbon as the 
chromium gives the metal a hardness similar to that given by carbon, 
but one which makes the cohesion of the molecules greater. This makes 
the metal much more homogeneous, and gives it the ability to resist shock 
and torsional stresses. Thus, this alloy is one of the best steels for crank- 
shafts of internal-combustion engines or other parts of machinery which 
have to withstand similar vibrational stresses. 



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Percentage of Chroniiunr 

Fig. 50. — Effect of chromium on tensile strength and elastic limit. 

The nickel-chrome steels are difficult to forge, as it is dangerous to 
hammer them after the temperatvu-e has dropped below that which makes 
the metal a bright yellow. It must be heated many times to forge pieces 
of any size or of intricate shapes. The chrome-vanadium steels, however, 
are no more difficult to forge or machine than the 0.40% carbon steels. 
Chrome steels for armor plate are made with the chromium content about 
2%, while as high as 6% is \ised in some of the high-speed steels when the 
tungsten or molj^bdenum content is high. 

TUNGSTEN 



Tungsten forms a large variety of compounds, two of which are ^vith 
oxygen, namely: the bioxide (WO,) and the trioxide (WO3). The trioxide 
forms salts with bases analogous to the molybdates. It occurs in nature 



INGREDIENTS OF AND MATERIALS USED IN STEEL 101 

as tungstates, the principal one of which is wolframite (FeW04), an iron, 
salt that always contains some manganese. It is very hard, difficult to 
fuse, and forms lustrous steel-colored laminae or a black powder. 

The tungsten metal has recently been used quite extensively for 
incandescent lamp filaments but was extremely brittle and hence 
hard to work. This brittleness was considered an inherent property 
of the metal that could not be overcome. While preparing this, 
however (April, 1910), ductile tungsten has been produced at a cost 
that is not prohibitive. This promises to make some radical change 
as when reduced several times in drawing it into fine wire, about 
.001 inch in diameter, a tensile strength of 610,000 pounds per square 
inch has been obtained. This is nearly double that of piano wire, 
the strongest metal known. 

Tungsten as an ingredient of steel has been known and used for a 
long time, it having been used in the celebrated Damascus steel, but its 
actual effect was not known until Robert Mushet, after much experiment- 
ing, brought out the famous "Mushet steel." This caused some radical 
changes in treating crucible steels, and much progress and improvement 
has been made since that time. 

Tungsten reacts on steel somewhat as does carbon, that is, it increases 
its hardness; but weight for weiglit carbon is superior in this regard to 
tungsten. If the percentage of tungsten is high with a proportionately 
high manganese content the steel can be hardened by cooling in the air. 
This is the direct opposite of the effect of carbon, and this fact Mr. Mushet 
used in his Avell-known steel. 

As the principal use of tungsten is in high-speed tool steel, and as a 
high percentage of manganese makes steel that is liable to fire crack, to 
be brittle, to be weak in the body and to be less easily forged and annealed,, 
the manganese is now kept low and chromium is used in its place. The 
timgsten-chromium steels when hardened retain their hardness when 
heated to a dull red by the friction and pressure of chips in cutting. This 
has led to the term "red-hardness" as applied to this class of steel, and 
it is this property which has increased the cutting speeds of tools. 

Tungsten when added to steel up to 7% does not make it any more 
self-hardening than the carbon tool steels if the manganese or chromium 
are low; but every increase up to 19% increases the red-hardness if 
chromium is increased proportionately. Beyond 19% of tungsten, the 
red-hardness is decreased no matter what the percentage of chromium 
may be. The increase in red-hardness is aljout 50%;, with an increase 
in tungsten from 6 to 19%, and that with manganese as low as 0.15%. 
With the chromium in the proper percentage tungsten will make steel 
self-hardening in all percentages over 0.85, but if the chromium is too 
high proportionately the steel is liable to become injured by overheating 



102 COMPOSITION AND HEAT-TREATMENT OF STEEL 

when the lower percentages of tungsten are used, but when the higher 
percentages of tungsten and chromium are used, the metal can be heated 
to just below the melting point and then quenched without injury. In 
fact, with the tungsten at 18% and the chromium 6% the best results 
for cutting tools are obtained when hardening at this high temperature. 

The carbon content of these steels is kept low as compared with ordi- 
nary tool steels, or the air-hardening steels of a few years ago; as the 
tungsten-chromium ingredients give steel a red-hardness. The carbon 
content in the high-speed steels of to-day usually varies between 0.65 
and 0.80%, whereas it was used in varying percentages up to 2.4 in the 
older air-hardening steels. This latter percentage was used in Mushet steel. 

The quality of red-hardness given steel by the tungsten-chromium 
ingredients increased the cutting speed of tools about 45% over that of 
the older air-hardening steels, when cutting hard forgings or castings. 
Similarly an increase of about 90% was made when cutting softer metals. 
This has led to their almost universal use to the exclusion of Mushet 
steel, which but a few years ago filled 50% of the sales of tool steel. 

Tungsten either in combination with manganese or chromium has 
greatly lessened the skill and knowledge required in heat-treating tool 
steel. To get the proper degree of red-hardness in the best grades of 
high-speed steel, they should be heated nearly to its melting point, which 
is about 2500° F. If this temperature were reached it would soften the 
steel so that the point of the tool would run. This would not harm the 
cutting qualities as it would not lessen the red-hardness given the metal 
by the tungsten and chromium. If a greater temperature were reached 
it would melt the steel, so it can easily be seen when the melting temper- 
ature is reached. On the other hand, if a temperature of 2300° F. is 
reached, the same red-hardness will be given the steel, so that there is a 
range of about 200° that will give the same results in heat-treating. 

The carbon tool steels, however, have to be heated to a few degrees 
above the recalescent point ami then quenched to obtain the greatest 
degree of hardness. After this they must be drawn to remove the brittle- 
ness caused by the high temperature. This requires a great deal of skill 
to judge the correct temperatures, as a variation of 25 degrees will make 
quite a difference in the temper and consequently in the cutting and 
wearing qualities. 

MOLYBDENUM 

Molybdenum, like tungsten, forms a large variety of compounds, 
among which are four oxygen compounds that include a mon-, bi-, and 
tri-oxide. It occurs, principally, in nature as molybdenite, which is the 
sulphide, M0S2, and as wulfenite, the lead molybdate (PbMo04;) also 
less frequently as the trioxide (M0O3). 



INGREDIENTS OF AND MATERIALS USED IN STEEL 103 

Molybdenum is often used in high-speed steels in place of tungsten, 
as its action is very similar. Where 2% of tungsten is used, 1% of molyb- 
denum will give the same results, that is, one molecule of molybdenum 
appears to have the same effect as one molecule of tungsten, its atomic 
weight being double that of tungsten. The cost of molybdenum is so 
much higher than that of tungsten that its use is prohibitive, unless much 
better results can be obtained, and a few high-speed steel makers are of 
this opinion, some using it in combination with tungsten. 

Many experiments have been made with molybdenum in place of 
tungsten, and molybdenum combined with tungsten, but these showed 
considerable irregularity in steels of the same chemical composition and 
heat-treated in the same way as the tungsten-chromium steels. The 
cause of these irregularities were not determined definitely, but the molyb- 
denum tools seemed to run at their highest cutting speeds when heat- 
treated at a lower temperature than the tungsten steels. This would 
indicate that the heat-treating would require more skill in judging the 
temperature as it is very difficult to judge a definite temperature by the 
color of the steel after it has passed a yellow. 

Molybdenum also has a tendency to make the steel more brittle, and, 
therefore, weaker in the body as well as giving it a tendency to fire-crack, 
which is a serious defect in tool steel. 

Uranium, which also belongs to this same chemical group, has stronger 
basic properties than either tuiigsten or molybdenum, and differs from 
chromium in that its trioxide forms salts with acids. These are the iiranyl 
salts derived from hydroxide, which forms salts with acids and with the 
strongest bases, and these are analogous to the composition of the bichro- 
mates. Uranium occurs chiefly in nature, in the mineral pitchblende, or 
uraninite, which consists of the oxide (UoOg), and this is heated in the elec- 
tric furnace with charcoal to isolate the metal. It has the color of nickel. 

Owing to the fact that uranium resembles nickel and has many of 
the characteristics of the other members of the chemical group to which 
it belongs, many experiments have been carried out to see if it could not 
be made a beneficial ingredient of steel. None of these experiments, 
however, have shown that it was as good as the other materials used 
daily in the composition of steel, and its chemical actions, as described 
above, would not make it appear that anything could be expected of this 
element that could not be obtained with cheaper materials, and some 
detrimental effects might be obtained. 

VANADIUM 

Vanadium occurs in nature in the form of vanadates or salts of vanadic 
acid (H3VO4), and this is analogous to phosphoric acid. When used in 
steel making it contains within itself no virtues, but acts as a physic on 



104 COMPOSITION AND HEAT-TREATMENT OF STEEL 

other elements, and is a powerful medicine. It gives the best results 
in the quaternary steels, such as vanadium-chromium-manganese-carbon, 
vanadium-nickel-manganese-carbon, and vanadium-tungsten-chromium- 
carbon. It has an affinity for oxygen and oxidizes out of the steel when- 
ever it comes in contact with this element. Therefore it has the property 
of elusiveness to a marked degree, and has to be handled carefully by 
the steelmakers in order to keep it in the finished metal. 

Vanadium renders possible the natural formation of the sorbitic struc- 
ture which makes the steel better able to withstand wear and erosion by 
adding to its self-lubricating properties. It retards the segregation of the 
carbides, which renders steel susceptible of great improvements by heat- 
treating. Vanadium produces soundness mechanically as well as chemi- 
cally and toughens the steel by acting as a physic on the other ingredients 
and scavenging out the oxides and occluded gases; by so doing it increases 
the molecular cohesion. The percentage of oxygen in the steel, however, 
should be reduced to a minimum by other materials, before adding the 
vanadium, and allow it to take care of what cannot otherwise be removed, 
as it is too expensive a material to use as a deoxidizer. 

As all substances deteriorate in time, or, in other words, reach the 
end of their career and die, we hear many terms applied to steel, such as 
"mysterious failure," "fatigue," "sudden rupture," etc., which in reality 
mean the end of the life of the molecules at the point of rupture. This 
is commonly called crystallization, as the molecules cease to cohere with 
one another and form into microscopic crystals. 

Vanadium seems to exercise a decided influence on these failures of 
steel by giving to the molecules a longer life. This makes the metal 
much better in its dynamic qualities, that is, resistance to repeated stresses, 
alternating stresses, and simple repeated or alternating impacts. Vana- 
dium also removes nitrogen, which is very detrimental to steel even in 
infinitesimal quantities. It also toughens the constituent called pcarlite 
and, when used in combination with chromium, reduces the mineral 
hardness given to steel by this element, so that it can be machined and 
forged as easily as an ordinary carbon steel. 

Vanadium has made great strides in the past few j^ears as an alloying 
element, and is used in steel castings, cast iron, and the bronzes and brasses, 
as well as in steel mill products. In one respect it is similar to carbon 
in that very small percentages give the desired results. It is used in 
percentages varying from 0.16 to 0.18 for the moving parts of machinery 
and springs, while for case-hardening steel, 0.12% is sufficient. In high- 
speed steels it has given good results in from 0.28 to 2%. If used in too 
large a quantity, that is, much over 0.30%, it dynamically poisons the 
metal, and the dynamic qualities for which vanadium steels are noted 
are rendered no better than, if as good as, the ordinarj^ carbon steels. In 



INGREDIENTS OF AND MATERIALS USED IN STEEL 105 

high-speed steel, however, the cutting qualities are considered of greater 
importance than the dynamic strengths, and the best high-speed steels 
that have been placed on the market contained 1% of vanadium. These 
steels increased the cutting quality of tool something over 10% when 
working on hard steel or castings. 

While the cost of vanadium-chrome steel is from 6 to 10 cents per 
pound, one firm, which builds gasolene engines, claims that it is no more 
expensive in actual practice than carbon steel, and is much cheaper than 
nickel steel, o^ving to the ease with which it is machined and forged, the 
lighter weight of the parts, owing to its great strength, and the greater 
accuracy obtainable, owing to the uniformity of the metal. 

Vanadium steel is used largely for crank-shafts, connecting rods, 
piston rods, axles, crank-pins, gears, gun barrels, springs, locomotive 
side frames, or other parts of moving machinery that are submitted to 
vibrational, impact or torsional strains and stresses. 

TITANIUM 

Titanium belongs to the same chemical group as silicon, and three 
other elements which are quite rare. In some respects it resembles 
carbon. It forms one compound with oxygen, namely, Ti02, and this 
titanium dioxide occurs in nature in three distinct forms. The principal 
one of these is the titaniferous ores that contain ferrous titanate 
(FeTiOa). 

In its natural combination with iron it is almost impossible to make 
it beneficial to the steel products. When separated in the electric fur- 
nace, however, and made into a ferro-titanium, that contains from 12 
to 15% titanic acid, about 6%, of carbon, and 5% of all other impurities, 
with the balance iron, it greatlj^ improves steel and iron, if added in the 
proper proportions. 

Titanium burns more energetically in oxygen than any kno^Mi sub- 
stance. When heated in oxygen it creates an instantaneous dazzling 
flame like lightning. Its combination with nitrogen gas is attended with 
the evolution of heat; it being the only undisputed example of the com- 
bustion of an element in nitrogen. While nickel, chromium, molbydenum, 
and tungsten add certain good qualities to steel, none of these combine 
with nitrogen and thus remove it from the metal as titanium does. 

Titanium has a great affinity for nitrogen and carries this off into 
the slag; nitrogen being, at least, as detrimental to the physical proper- 
ties of steel as phosphorus, and present in larger percentages than has 
hitherto been supposed. It affinitizes to a slighth^ lesser degree with 
oxygen and removes this also. While sulphur and phosphorus are not 
removed to any great extent by titanium, by removing the oxygen and 



106 COMPOSITION AND HEAT-TREATMENT OF STEEL 

nitrogen it prevents these from forming oxides and nitrides, and these 
are the real injurious substances. Titanium by combining with the gaseous 
nitrogen forms a stable nitride that shows as tiny red crystals under the 
microscope. This it carries off into the slag and greatly increases the 
quantity that is removed or lifted from the molten metal. Unless an 
unnecessary quantity of the alloy is used, the titanium itself passes off 
with the slag, and will not show on the analysis of the metal. The titanium 
itself is of no special benefit as a component of the finished steel, and only 
enough should be used to remove the impurities. Any excess above 
this will remain in the steel, and if proof is wanted that one is buying a 
titanium-treated metal, enough of the alloy could be used to show by 
analysis, as a small percentage left in the steel is not harmful. 

One instance of the removal of nitrogen was shown in some ordinary 
Bessemer steel rails that were found to contam from .013 to .015% of 
nitrogen. When 0.50% of ferro-titanium, containing 15% of titanic acid, 
was added, the nitrogen was reduced to from 0.004 to 0.005%. As it 
also has a strong affinity for oxygen it provides a simple means of 
thoroughly deoxidizing steel. 

Titanium, by removing the oxygen and nitrogen, prevents the forma- 
tion of blow-holes in steel. It also reduces the size of the pipe, as it makes 
the bath more liquid by freeing it from the free oxide and slag. This 
makes the metal subside in the mold while cooling, and the pipe will 
be smaller and flatter. It also makes it roll well. In this connection the 
record of a day's work in rolling, as taken from a pyrometer, showed an 
increase of not less than 30° F. in the heat of the metal at a given point. 
That is, 30° above that of untreated metal at the same point, while passing 
through the roll. The metal almost invariably does not boil but lays 
dead in the ingot molds. 

Due to the removal of nitrogen and oxygen from the steel, the physical 
properties are improved and its density increased. The tensile strength, 
elastic limit, reduction of area, transverse strength, hardness, elasticity, 
wearing qualities, resistance to shocks, and torsion, are greatly improved. 
Thus titanium gives practically the same results as vanadium, and the 
ferro-titanium can be produced for a fraction of the cost. One example 
of its ability to withstand torsional strains was shown with a bar 4 feet 
long and 1| inches square. This was twisted through seven complete 
revolutions without the sign of a fracture. The Brinell hardness test 
shows titanium steel to be softer than ordinary steel rails of the same 
analysis and section, and this is probably due to the finely divided ferrite 
network. 

A ferro-titanium alloy that contains from 10 to 15% of titanic acid 
gives the best results, as this goes into almost instant solution. When 
a higher percentage is used the titanium is always liable to segregate, 



INGREDIENTS OF AND MATERIALS USED IN STEEL 107 

as it has a much higher melting point than that of steel. Thus when a 
25% alloy was tried nothing was gained by its use. When, however, 
an alloy is used that will allow the titanium to enter into solution in the 
molten metal it retards the segregation of the other ingredients and 
produces a very homogenous steel. 

One per cent of the 10 to 15% ferro-titanium alloy is all that is neces- 
sary to add to the steel, as this amount will seize all of the nitrogen and 
probably all of the oxygen that has been left in the bath. In many cases 
this can be reduced to one-half of 1%, and after some experience in its 
use the one-half of 1% might be sufficient for all steels. This small 
amount removes the bulk of the blow-holes and segregation found in 
Bessemer steel, and in the case of steel rails it only increases their cost 
about $2 per ton. With the titanium steel rails numerous use tests have 
been made, and all of these prove that they wear about three times as 
long as the ordinary steel rails, while in some cases they have outworn 
six of the Bessemer rails. 

In the Bessemer and open-hearth process of steel making it is always 
best to add the ferro-titanium in the ladle. It should be shoveled in 
loosely, and never preheated, but used cold. The first shovelful should 
be put in after the bottom of the ladle is well covered with molten metal 
and after the ferro-manganese has been added, when this is put in the ladle. 
One shovelful at a time should then be put in while the ladle is filling, 
so as to give it the benefit of the swirling and churning motion of the 
molten mass. The last shovelful should be added before the ladle is 
three-quarters full. One reason for this is that the alloy is lighter than 
iron and would not sink and disseminate through the bath if it were 
added near the top. Another reason is that if it were near the slag it 
would unite with the nitrogen in the slag and consequently would not 
benefit the metal. 

The alloy should never be used in connection with aluminum, as alumi- 
num adds brittleness and titanium removes brittleness, hence the two 
alloys are antagonistic, and the titanium will do its work much better 
alone. 

In crucible steel making it is sometimes preferable to add the titanium 
alloy with the charge of metal that is to be melted down, and in this case 
it should be added well down toward the bottom of the crucible. It has, 
however, been successfully added after the metal is boiling and when the 
manganese is added. At this time the titanium alloy should be added 
after the manganese. In fact, at all times it should be the last material 
added to the bath. 

After adding the alloy the ladle of metal should be held for from 5 
to 15 minutes before pouring, in order to allow the titanium to do its 
work and scavenge out the oxygen and nitrogen. There is no danger of 



108" COMPOSITION AND HEAT-TREATMENT OF STEEL 

the metal in the ladle becoming chilled by holding it, as the redction caused 
by titanium causes its temperature to rise rather than lower, and the 
metal is in better condition for pouring after standing than before. In 
one case a ladle of steel was held for 20 minutes after tapping and adding 
the titanium, and it was then in better condition for pouring into ingots 
than is steel without titanium soon after it is tapped. The increased heat 
of the molten metal, due to the reaction of titanium, ranges from 50° to 
90° F. above that of ordinary steel held in the ladle for the same length 
of time. 

Titanium also prevents steel from heating up as quickly as the steels 
in which it is not used. An instance of this was some titanium-treated 
ingot molds that did not show red in the dark when filled with moiten 
steel, whereas, the ordinary ingot molds, standing beside them, were 
distinctly red hot. The metal is also comparatively slow in heating from 
friction, and this is one of the causes whj^ metals treated with it are nmch 
more durable than others. Steels treated with titanium heat up more 
slowly than others when machining them. The cutting speed can there- 
fore be increased, and the machine work done more quickly. This also 
makes it very advantageous to use in tool steels; whether of the carbon 
or high-speed kind. 

Owing to the fact that titanium inci-eases the heat of the molten metal 
to a very markeil degree, it is seldom necessary to use much ferro-silicon, 
as silicon is largely used for this purpose. Silicon, however, is not so 
efficacious and is known, at times, to precipitate phosphorus with disas- 
trous results. Thus, when titanium is used the proportion of ferro-silicon 
should be decreased and, if possible, eliminated entirely. If not eliminated 
entirely, it could be reduced from time to time until no further improve- 
ment is noticed. If defects are found in the surface of the finished steel, 
a slight increase in the ferro-manganese and a decided decrease in the 
ferro-silicon used will overcome that. 

Steel castings that have been treated with titanium are more blue in 
color, free from blow-holes and brittleness, and heat less under cutting 
tools than ordinary steel castings; thus they can be machined more easily 
and rapidly. The transverse strength has been increased from 17 to 
23% by its use. 

Titanium increases the breaking strains, wearing qualities, and hard- 
ness in the chill of cast iron, and hence is very beneficial for such castings 
as car-wheels, but it decreases the chilling effect. 

Titanium also promises some good results when used in copper, brass, 
or bronze, in which case a cupro-titanium instead of a ferro-titanium is 
used. This has been used in about the same proportions as the ferro, 
but the best results have been obtained in copper with from H to 2% 
of the cupro-titanium. 



INGREDIENTS OF AND MATERIALS USED IN STEEL 



109 



ALUMINUM 

Aluminum is the third largest element in the earth's crust, and com- 
prises 7.81% of it. It occurs widely distributed and in many forms of 
combination; one of the most common of which is clay, where it exists 
in various conditions of purity. It is only within the last few years, 
however, that it could be separated from its impurities cheaply enough to 
make it a commercial metal. 

Since aluminum has come into prominence in metallurgy it has found 
many uses, and one of these is in the making of steel. This element, 
however, is only used as a purifier, as it adds nothing to the strength of 
steel except in so far as it removes some of the impurities. 

Aluminum suppresses the evolution of gas either by increasing the 
metal's solvent power for that gas or by removing the oxygen, and thus 






ess 

S CO. 
C to -^ ■ 



= - w 







0.15 






■ 0.20 






Percentage 
0.25 


of Carton 














0.22 




4U 




\, 










































_ 










30 








" 














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-=^ 





















— 




20 




























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i»^ 


— - 


■ 


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10 







































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1 2 3 4 6 6 

Percentage o£ Aluminum 

Fig. 5L — Effect of aluminum on steel. 

preventing the later formation, carbonic oxide, or by both means jointly. 
This makes the metal more dense by removing the microscopic bubbles 
formed, and greatly decreases the tendency of segregation as the aluminum 
has a quieting effect on the molten metal and the carbon, phosphorus, 
and sulphur form compounds with the iron which are lighter than the 
molten metal and have a tendency to rise to the top. 

Only enough aluminum is used to cause this effect, and thereafter 
work out of the metal. If solid alumina is produced it is liable to remain 
suspended in the metal and cause a lack of continuity of the metallic 
structure, and thus a loss of strength. 

Fig. 51 shows the effect of aluminum on the tensile strength, elastic 
limit, and elongation of steel with various percentages of carbon. 

OTHER ALLOYING ELEMENTS 



Some tin steels have been made. These cannot be rolled. If there 
be more than 1% of tin present they are extremely hard and brittle. 
Annealing has the same effect upon these as upon the ordinary steels ;^ 



110 COMPOSITION AND HEAT-TREATMENT OF STEEL 

there is in no case precipitation of the carbon in the state of graphite. 
Hardening produces martensite only where there is peariite beforehand; 
it seems that the ferro-stannide solution of iron does not dissolve the car- 
bon. 

Yttrium has been mentioned as an alloying element for steel, but it 
is only found in combination with a few rare minerals, and consequently 
is only seen in the laboratory. It belongs to the same chemical group 
as aluminum, and if it were found to be beneficial to steel it could not be 
obtained in sufficient quantities for commercial use. 

Cerium and lanthanum have been combined with iron in the electric 
furnace to make an alloy that will give off luminous sparks. The maxi- 
mum sparking effect seems to be obtained with about 50% of iron, and this 
will light illuminating gas. The sparks are obtained by striking the alloy 
with steel similar to the way flint was used before the days of matches. 
Some such combination might be used for generating the spark in internal- 
combustion engines. One such alloy was sold to the match trust and 
killed, as they feared competition from its use. 



CHAPTER VII 

Working Steel into Shape 

Rolling 

After the iron ore has been reduced to pig metal, and this combined 
with the other ingredients that go into the making of the different grades 
of steel, and the whole refined in the various kinds of furnaces used and 
then cast into ingots, the ingots are sent through slabbing rolls, as shown 
in Figs. 52 and 53. The slabs thus formed are then rolled into the numer- 
ous shapes that are used for manufacturing purposes. 

The slabbing mill, with a single pair of rolls and stationary table, 
which is used by many steel makers, is shown in Fig. 52. In Fig. 16 is 
shown the mechanically operated grip that has just brought an ingot from 
the soaking pit, and dropped it onto the carrier that conveys it to the rolls, 
and Fig. 17 shows the same ingot just as it has made its first pass through 
the slabbing mill. After this the mill is reversed and the ingot passes 
back through another section of the rolls to further reduce it. After 
some four or five passes back and forth through the rolls, during which 
time it is turned over so as to roll all four sides, it is sent to other rolls 
that reduce it to commercial shapes. 

In Fig. 53 is shown the tilting table and pulpit mill, that was first 
brought out in Germany. This has a double set of rolls, and for the 
first pass of the ingot the end of the table next to the rolls is lowered 
to receive it as it comes through. The mill is then reversed, and 
while reversing the end of the table is elevated, as shoT\'n in the illustra- 
tion, and the ingot sent back through the upper rolls. The rolls, as 
well as the tilting table, are controlled from the platform of the pulpit, 
shown to the right of the picture. In this design a much narrower mill 
can be used for the same number of passes than in the design of mill 
shown in Fig. 52. 

After slabbing the metal, various kinds of rolling mills are used to get 
the steel into the shapes desired. Many times the different mills are 
combined so as to make the rolling operations continuous from the steel 
furnace to the finished product. In some cases the ingot molds are removed 
as soon as the ingot is cool enough for rolling, and the desired shape is 
finished before the metal has had time to cool off after leaving the fur- 
Ill 



112 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




o 



03 
O 

a 



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CI 



WORKING STEEL INTO SHAPE 



113 




T3 

a 



n 

Pi 



o 



114 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



nace in which it was refined and mixed. In Fig. 54 is shown the metal 
being reduced to rods in a wire mill, and the kind of rolls used. Here 
the rods run into a track as they leave the rolls, and this guides them to 
the next roll that further reduces the metal in size. 



CRYSTALLINE STRUCTURE OF METAL 



Steel that has cooled slowly from the liquid state, as is the case with 
that which has been cast into ingots from the converter, furnace, or cru- 
cible, forms into crystals which do not show the same structure throughout. 




Fig. 54. — Rod rolls with track and water-cooled rolls. 



The outer shell of the ingot will have a different structure from the rest 
of the mass due to its cooling quickly, and therefore it is under strains 
until the center of the ingot has cooled. The top of the ingot also has 
an area of abnormal crystallization which is due to segregation. There 
is, however, the same general crystalline character in the largest part 
of the ingot. 

In passing the steel between rolls, to reduce it to the sizes and shapes 
wanted in the finished machine, this crystalline grain is broken up and a 
new grain which is much finer takes its place if the temperature of the 
metal during rolling has been kept slightly above its highest point of 
transformation, as at or just above this point a new grain structure is 
born which makes the metal more homogeneous. 

This formation of grain continues after the steel leaves the rolls until 



WORKING STEEL INTO SHAPE 115 

it has cooled below its lowest point of transformation, at which point it 
sets, and no more change will take place until the metal is heated to the 
critical point again. 

In rolling steel it is frequently heated to from 2000° to 2400° F., and 
it would seem that this would seriously damage it. This would be so 
if it were not for the fact that the mechanical pressure exerted upon the 
metal by the rolls breaks down the large crystals formed by this high 
temperature and reduces them to a small size. The final size of the crys- 
tals is, therefore, dependent upon the temperature of the steel at the 
finish of the rolling process. 

Finished steel has a finer grain structure if the last rolling operation 
receives the metal at a temperature which is falling from 1650° F. to 
1400°, which are the highest and lowest points of transformation, than 
if it is finished at 2000° F., or any temperature above the highest point 
of transformation. On the other hand, if the rolling be continued after 
the temperature of the steel has fallen below the lowest point of trans- 
formation, strains are set up which make the piece unfit for use until it 
has been thoroughly annealed. 

KULES FOR ROLLING 

Four rules might be established in rolling steels which will affect the 
final size of the grain so as to make it what it should be, and these are: 

First. — The rolling operations should be continuous from the highest 
temperature employed down to the finishing temperatures, as long waits, 
such as are generally made necessary when the metal is formed roughly 
to shape and size at a high heat, then allowed to cool and a little work 
done upon it at the lower temperature, are liable to cause a coarse grain 
that cannot be made fine by the last rolling. 

Second. — There are better results obtained if the steel is passed 
several times through the rolls with a small reduction in the size of the 
metal each time, than if a large reduction is made with a very few passes. 

Third. — In rolling a large piece a great reduction can be made during 
the first pass through the rolls, and the amount of reduction gradually 
decreased with each passage through the rolls until the finishing roll 
gives it just the right amount of reduction conducive to the making of 
the grain as fine as the steel will assume. 

Fourth. — The steel should reach the finishing roll so that the tem- 
perature will be falling, from 1650° F. to 1400° while it is passing through 
the rolls. It should not be allowed to go below 1300° until all the rolling 
operations have been finished. 



116 COMPOSITION AND HEAT-TREATMENT OF STEEL 

HIGH AND LOW TEMPERATURES 

Steel is so mobile at very high temperatures that it yields to distortion 
by the crystals sliding past one another, but as the temperature decreases 
the mobility of the mass becomes less, and less sliding is possible. The 
crystals then crush against each other, and at the lower temperatures a 
crushing of the crystals only takes place. 

To obtain the very best qualities in a 0.50% carbon steel that it is 
possible to produce, the work of rolling should be completed just at the 
time when the ferrite begins to separate from solid solution. Rolling 
the work below the temperature at which this occurs, which is while the 
metal is cooling from 1650° F. to about 1300°, greatly increases the brittle- 
ness of the metal. Rolling the steel at a higher temperature lowers 
the strength, owing to the coarser grain which is given the metal. For 
steels of all other carbon contents it is logical to assume that the same 
rules hold good, but it is possible, although not probable, that further 
investigations may change them. 

Steels are rolled in a large variety of standard shapes, such as round, 
square, oblong, hexagon, octagon, tubes, and L, T, U, I shapes, etc., and 
can be obtained in nearly any special shape desired, providing enough 
is wanted to pay for the making of rolls. 

Casting 

APPARATUS FOR MELTING 

Casting steel consists of pouring the metal in a fluid state into molds 
which give it the desired shape. These shapes can be given most any 
kind of an intricate form owing to the shape being given the mold by a 
pattern and cores. 

Many different methods are used for melting the steel, and some of 
these are the same in principle as those used for converting the blast- 
furnace metal into steel. 

The cupola has been used to a large extent, but does not give good 
results, as the metal is much altered in remelting by the alterations in 
temperature and the exposure of the metal. The change in the metal 
is made by the absorption of the carbon and changes in the silicon and 
manganese. 

Pig iron and steel are melted together in the cupola, but this is not 
a normal product. It might be called a hybrid metal which is useful for 
special purposes, but fundamentally different from any kind of steel. 
It is a httle better than cast iron, and is a very cheap mixture compara- 
tively. 

The open-hearth furnace is used a great deal for melting steel, for 



WORKING STEEL INTO SHAPE 117 

steel castings, and might be considered the cheapest method of turning 
legitimate steel into castings. Scrap steel and iron are used in this fur- 
nace, but they are melted under an oxidizing flame, and the metalloids 
are almost entirely eliminated, thus giving a definite starting point from 
which a known and regular metal can be made by the addition of recar- 
burizei's. In this country the acid open-hearth furnace is nearly always 
used, but in Germany many basic open-hearth furnaces are used. 

The Bessemer converter with a variation that is called the Tropenas 
process is used by many for making steel castings, and this if properly 
run gives good results in the castings. In the Bessemer converter the 
blast is blown in at the bottom, while in the Tropenas process the air 
is blown at a low pressure upon the surface of the molten metal. Some 
four to seven inches above this set of tuyeres is another set, which sup- 
plies air to burn the carbonic oxide, the upper set not being operated until 
the blowing is well under way. Some have adopted side blowing in this 
style of converter. It creates a greater amount of heat owing to the 
more perfect oxidation of carbon and a burning of a proportion of iron. 

The crucible process has been used to some extent for small castings, 
and to cast some of the special alloyed steels. Its condition of "dead- 
melt" gives a more quiet metal, generates less gas when the metal comes 
in contact with cold surfaces, and the castings are more liable to be free 
from blow-holes; in fact, a German foundrj^ by using special care in the 
mixing of the metal, melting it, and making the molds, guarantees castings 
free from blow-holes, and makes castings of any composition of metal 
from wrought iron to high-carbon or high-speed steels. 

This method produces the best steel castings, but it is the most expen- 
sive way of making them. 

The electric furnace is just beginning to be used for melting the metal 
for steel castings, but it promises very good results as the phosphorus 
and sulphur can be reduced to a trace, and the oxygen and nitrogen can 
be very materially reduced. 

RISERS, GATES, ETC. 

In making steel castings about 40% of the melt is used to supply 
risers, sprues, gates, etc., and there is consequently a loss in remelting 
these. 

The risers, which are sometimes called sink-heads, run from the top 
of the mold to the casting and are put on all thick sections of the casting 
to feed the metal to it while it is cooling and shrinking. These must be 
kept from solidifying until after the casting has become solid by con- 
tinually stirring with an iron rod. 

The sprae is the name given the opening into which the metal is poured, 
and this runs from a pocket in the top of the mold to another pocket, 



118 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



which is usually located near the bottom of the casting. From this lower 
pocket to the opening in the mold, which is to form the casting, are cut 
other openings so the metal will be able to flow in. These openings are 
called gates. This arrangement is made necessary to prevent the liquid 
metal from tearing up the mold, as it would do if poured directly into 
the opening that forms the casting. The metal left in these when the 
casting is poured has to be broken away from and chipped and sawed off 
of the casting. They are then remelted to make other castings. 

COMPOSITION OF STEEL CASTINGS 

Steels with various alloying materials and of numerous different com- 
positions are being used for castings to-day. The carbon content of 
these varies with the use to which the casting is to be put. Over 0.70% 
carbon is seldom used in castings, owing to its making the steel too hard 
to machine, and in complicated shapes the shrinkage cracks are liable 
to become dangerous. 

In the ordinary steel castings manganese should not exceed 0.70% 
for soft castings and 0.80% for hard ones, as more than this is liable to 
make the metal crack when shocks are applied to it. Silicon may have 
a percentage of 0.10 in the soft castings, and 0.35% in hard ones without 
diminishing the toughness. Aluminum is used by many in making cast- 
ings, as it has a great affinity for oxygen, and will remove the last trace 
of this from the iron. It also aids in dissolving the gases. It has a ten- 
dency to make the metal sluggish, but it enables it the better to run through 
small passages as without it the metal foams and froths when it comes 
in contact with cold surfaces, thus impeding the flow and chilling the 
advance guard of the stream. Aluminum should oxidize out of the steel, 
and not show over 0.20% when the steel is analyzed, but it is better if 
only traces are left, as it decreases the ductility. 

Sometimes the phosphorus is allowed to be as high as 0.08%, but when 
the castings are to be submitted to physical test the phosphorus and sul- 
phur should be kept below 0.05%. 

The physical properties of ordinary steel castings should be above 
the figures in the following table: 





Hard 

Castings 


Medium 
Castings 


Soft 
Castings 


Tensile strength in lb. per square inch 

Elastic limit in lb. per square inch 

Elongation percentage in 2 inches 


85,000 

38,500 

15 

20 


70,000 

31,500 

18 

25 


60,000 

27,000 

22 


Reduction of area per cent 


30 



WORKING STEEL INTO SHAPE 119 

A chemical composition which has given good results for locomotive 
side frames analyzed as follows: 

Carbon 0.27 per cent 

Manganese 0.57 " " 

Silicon 0.26 " 

Phosphorus 0.048 " 

Sulphur 0.033 " " 

Test bars from this showed a tensile strength of 68,870 pounds per 
square inch, an elastic limit of 36,450 pounds per square inch, an elonga- 
tion of 20% and alternating vibrations of 4707. 

VANADIUM-STEEL CASTINGS 

Vanadium has given such good results in rolled steels that it has been 
taken up by some of the steel foundries. In one case the usual mixture 
gave a steel showing a tensile strength of 68,580 per square inch, an elastic 
limit of 36,290 pounds, an elongation of 20%, and resistance to alternating 
vibrations of 4706. To the above mixture was added 0.22% of vanadium. 
With this product added the following strengths were obtained: tensile 
strength, 77,160 pounds per square inch, elastic limit 46,450 pounds per 
square inch, elongation in 2 inches 20%, and resistance to alternating 
vibrations, 14,971. It also increased the breaking strength to more than 
double and in some cases treble that of the ordinary steel. 

It is in the vibrational stresses that vanadium shows its great supe- 
riority, and these tests were made on an alternating bending machine by 
gripping the test bar rigidly at one end and bending the free end upward 
and downward | inch from its axis. It gave a total length of stroke of 
J inch, and this at the rate of about 30 strokes per minute. 

Before adding the vanadium in the furnace it is necessary to have the 
oxides all removed from the metal, as the vanadium has a great affinity 
for oxjfgen. If any of the oxides remain in the metal, the vanadium 
will scavenge them out and go off in the slag, owing to its great elusive- 
ness; but as vanadium is too expensive to use as a scavenger, the oxides 
should be removed before it is added to the steel. 

Many failures in the use of vanadium in the past have been due to 
this elusiveness or its affinity for oxygen, as many thought that if they 
put the vanadium in the steel, it must be there after pouring. As a matter 
of fact, it might have completely oxidized out of the metal and not given 
it any of the desirable properties it is capable of. 

With the oxides removed and other necessary precautions taken, 
the vanadium can be added with an assurance that it will be in the metal 
when analyzed; or more correctly speaking, that 90% of it will show on 
analysis, as a loss of more than 10% in the melting is uncalled for. 



120 COMPOSITION AND HEAT-TREATMENT OF STEEL 

In using the acid open-hearth furnace for melting steel, the vanadium 
is added to the mixture just before tapping. The slag is raked from the 
top of the molten metal, the ferro-vanadium thrown in and the whole 
allowed to stand a few minutes, so that the vanadium will thoroughly 
mix with the metal. 

As about 40% of the steel melted for castings goes back to the fur- 
nace, in the shape of risers, gates, and sprues, to be remelted, the vanadium 
is lost in these, owing to its oxidizing out during the melting process. 

TITANIUM 

Owing to the difficulty of obtaining the ferro-titanium, up to the pres- 
ent time, it has not been used to any extent in steel castings. Owing to 
its great affinity for nitrogen and a slightly lesser desire to combine with 
oxygen, it removes these from the metal. This should make the steel 
castings free from blow-holes, and make a more homogeneous metal. 
That it does increase the static and dynamic strengths, as well as the 
wearing qualities of steel, without increasing the hardness, has been amply 
proven. 

The ferro-titanium is not an expensive alloying material, and, as it 
is best to add it to the ladle after tapping, it is easy to handle without 
greatly increasing the cost of castings. After adding the ferro-titanium 
the ladle of metal should be held about six minutes before pouring the 
molds, in order to give the titanium a chance to do its work. This does 
not chill it, as might be supposed, as the temperature of the molten metal 
is raised by the titanium, and it will pour much more freely and smoothly 
at the end of the six minutes than a ladle full of ordinary steel will directly 
after tapping. It also adds some good properties to iron castings. 

NICKEL-STEEL CASTINGS 

Nickel added to steel in percentages of from 1.50 to 3.50 combines a 
high tensile strength and hardness, and a very high elastic limit with 
great ductility; therefore it is being used for steel castings with good results. 

For some time it has been cast in large castings, such as rolling mill 
gears and pinions, and it is now being cast by a few foundries in small 
castings such as are used for automobile parts. It is difficult to cast 
in castings that have a thinner section in any of their webs, ribs, etc., 
than I of an inch. 

The ductility which lessens the tendency to break when overstrained 
or distorted, combined with the very high elastic limit, makes it valuable 
for such parts as crank-shafts on internal-combustion engines. These 
have been cast of nickel steel and given satisfaction in use, although 



WORKING STEEL INTO SHAPE 121 

forgings are much better for this purpose. Front axles, of I-beam section, 
have also been used successfully on automobiles. 

Nickel-steel castings show a tensile strength of from 78,000 to 88,000 
pounds per square inch, an elastic limit of from 50,000 to 58,000 pounds 
per square inch, an elongation in two inches of from 25 to 30%, and a reduc- 
tion in area of 40 to 48%. This brings the elastic limit up nearer to the 
tensile strength than in the ordinary steel castings as well as increasing 
this and the elongation and reduction of area. This would indicate a 
greater resistance to shock and compression and the rendering of castings 
that are more ductile and tough than those made of the ordinary steel. 

DIRECT STEEL CASTINGS 

In this process the metal is taken direct from the furnace to a heated 
mixer where the proper materials are added to make the required quality 
of steel. The metal can be kept liquid as long as desired in the mixer, 
and its chemical properties adjusted by the addition of different materials. 
The mixer is kept full by transferring metal from the furnace. When 
the metal is wanted for casting the mixer is tapped and the metal run 
into ladles from which it is poured into the molds as in other castings. 

This process does away with the remelting of the metal in a cupola, 
converter, open-hearth furnace, or crucible, and its consequent losses 
from shrinkage. It produces a better and finer grained metal by the 
mixer reducing the gases which come in contact with the metal in the 
cupola or furnace. 

Castings of direct steel can be obtained with guaranteed physical 
properties as follows: tensile strength, 70,000 pounds per square inch; 
elastic limit, 35,000 pounds per square inch; elongation in 2 inches, 25%, 
and reduction of area, 40%. 

These castings can be forged, welded and case-hardened, and will 
machine as easily as machinery steel. They can also be bent freely when 
cold before breaking. 

MANGANESE STEEL CASTINGS 

Manganese steel with the manganese ranging from 12 to 15%, and 
the carbon contents high, is being successfully cast and used for such 
parts as have to resist wear from gritty substances such as are encoun- 
tered in rock crushers or in machinery used around concentrators. 

Manganese steel has the peculiar properties of being so hard that 
it cannot be machined in combination with a malleability which enables 
it to be headed cold when made into rivets, and a toughness which 
gives it remarkable ability to resist wear and shock stresses as well 
as cold bending. 



122 COMPOSITION AND HEAT-TREATMENT OF STEEL 

When they leave the mold manganese steel castings are much more 
brittle than cast iron, but by heating them to about 1650° F. and quench- 
ing in water, they are given their properties of great toughness and duc- 
tility. 

Owing to their being too hard to machine, all finishing must be done 
by grinding, but where it is desired to make a fit by machining, such as 
boring out a hub, a piece of metal that can be machined is placed in the 
mold and the manganese steel poured around it. By making this piece 
with numerous fins the manganese steel will shrink around it so that it 
will be nearly as firm as a solid casting. 

The gases generated in pouring the metal are so low that the molds 
ean be rammed very hard and mth a fine sand. In this way surfaces 
are obtained that are nearly as smooth as finished castings, and but little 
grinding is required when a finished surface is desired. 

Its shrinkage is about double that of ordinary steel when cast, and 
it cannot be cast in any very intricate shapes, nor can it be cast in any 
section which is thinner than J of an inch. 

When properly heat-treated manganese steel castings will show a ten- 
sile strength of 140,000 pounds per square inch, an elastic limit of 55,000 
pounds per square inch and an elongation in 2 inches of 45%. 

CHROME STEEL CASTINGS 

Where a great hardness is desired such as that required in the manu- 
facture of projectiles, chromium is added to steel that is to be cast. This 
gives the metal a mineral hardness that cannot be obtained with any 
other alloying material, and also refines the grain. 

The uses to which these castings can be put is limited, however, owing 
to the difficulty of machining. The castings cannot be made in any 
intricate shapes or thin sections, owing to the difficulty of making the 
metal flow easily, but for such things as projectiles no better steel has 
been found for casting, and its usefulness is increasing. 

Forging 

For those parts which cannot be produced from the rolling-mill shapes, 
or have not the proper strength when made in castings, forging is resorted 
to and there are several different ways of turning out these forgings: 
by hand, under a steam hammer, in a hydraulic press, or in a drop-forging 
press. The cost of these different methods of production depends largely 
on the number of pieces required of the same shape, but the size of the 
piece to be forged, as well as the components of the steel, have an influence 
on which is the best as well as the cheapest method to use. 



WORKING STEEL INTO SHAPE 123 



FORGEABILITY OF DIFFERENT STEELS 

Some of the special alloy steels are very difficult to forge. Chromium 
steel is the most difficult of all, owing to its producing a mineral hardness 
in the metal. If kept above 2200° F., however, it can be forged success- 
fully, and it should never be allowed to fall below this. Nickel added 
to this steel, giving nickel-chrome steel, makes it slightly easier to forge, 
but even then the metal should be kept at a bright yellow color during 
the forging operations. As steel melts at 2500° F., this means that a 
forging of any size will need reheating several times before it is completely 
formed into shape. Nickel steels are more easily forged than those men- 
tioned above, but they must be handled carefully, owing to the tendency 
of fissures to appear. 

The vanadium steels are more easily forged than either of these, and 
if due care is taken to increase the heat gradually at first — that is, 
this steel should not be plunged into the heat all at once — no trouble 
will be experienced afterward. Titanium steel is similar to vanadium as 
to its forgeability, but it heats up more slowly and retains a forging 
heat longer. It also has less of the "hot-short" property than other 
steels, and hence should forge well. 

Silicon in small percentages does not affect the forgeability of steel, 
but in large amounts it gives steel a fibrous grain, and is therefore used 
principally for springs. But in the last few years this steel has been forged 
into gear blanks to quite an extent. In this case the blanks should be 
made in the form of forged rolls, and not cut from bars, in ordei' to avoid 
the fibrous structure. 

The aluminum, tungsten, manganese, and other alloyed steels are 
not used to any extent for forgings, as those before mentioned show superior 
qualities, and some of the last named are much higher in price. 

Some of the carbon steels, particularly those that are high in carbon, 
cannot be heated to a temperature over 1800° F., without burning 
the metal, and when once burned it cannot be returned to its former 
state without remelting. A vanadium-chrome steel will give as great 
strength as a nickel-chrome, and can be forged as easily as a 0.40% 
carbon steel. 

The higher the carbon content the more danger there is of burning, 
and a steel with 1% of carbon is very difficult to forge at all, owing to 
the comparatively low temperature to which it is possible to heat it, and 
the comparatively high temperature at which the forging operations 
must be finished without danger of cracking the piece, owing to its brittle- 
ness. Thus high carbon steel should not have the heat fall much below 
its highest point of recalescence, which is above 1650° F., during any 
of the forging operations. Those forgings will be strongest that are 



124 COMPOSITION AND HEAT-TREATMENT OF STEEL 

finished just as the temperature reaches this point. The smith must 
also regulate the weight and effect of the blows so that the forging will 
be finished just as it reaches this point. This will prevent the formation 
of large crystals, give the piece a dense, homogeneous grain with the 
atoms holding together by a high cohesive force and result in the steel 
having an increased strength. Any kind of steel can be forged if the 
proper temperature is maintained while passing it through the different 
forging operations, and the forgings will be much stronger than steel 
castings, and in many cases stronger than rolled steel. 

Thanks to the electric and autogeneous welding process in combina- 
tion with die-forging with either the drop hammer or the hydraulic press, 
all of the highest grades of alloyed steel can be turned into forgings suc- 
cessfully, and their strengths and elongation retained, but this is almost 
impossible by the hand or hammer-forging methods, especially if welds 
are made necessary by the shape of the piece. One of the alloy steels 
that is being manufactured into die forgings has the following chemical 
composition: chromium, 1.50%; nickel, 3.50%; carbon, 0.25%; silicon, 
0.25%; manganese, 0.40%o; phosphorus, 0.025%; sulphur, 0.03%. 

In the annealed state this shows the following physical characteris- 
tics: tensile strength, 120,000 pounds per square inch; elastic limit, 
105,000 pounds per square inch; elongation in 2 inches, 20%; reduction 
of area, 58%. 

When properly heat-treated, that is, quenched in oil and drawn, these 
characteristics became: tensile strength, 202,000 pounds per square inch; 
elastic limit, 180,000 pounds per square inch; elongation in 2 inches, 
12%; reduction of area, 34%. 

EFFECT OF TEMPERATURE ON THE GRAIN 

The high temperatures, of from 2000° to 2400°, that steels are sub- 
jected to when forging would seem to indicate that the metal is weakened 
by overheating, but such is not the case, as forgings show greater strength 
than the same metal formed into shape in any other way, unless it be 
the rolled steels. 

Steel, when heated to the above temperatures, coarsens in grain and 
the grain becomes crystalline in nature. This makes it so mobile that 
it yields to distortion by the crystals sliding past one another, but as 
the temperature decreases the mobility of the mass becomes less, and less 
sliding is possible. If then forged the crystals would crush against each 
other; and when cool the crystals themselves will crush. 

These coarse crystals, that are formed by the high temperatures, are 
reduced by the hammering process in the drop-hammer press, or the 
squeezing process in the hydraulic press, until the crystalline structure 
is broken up and a new grain that is much finer takes its place. 



WORKING STEEL INTO SHAPE 125 

If the piece is not allowed to cool below its highest recalescence point 
during the forging, and the forging is finished just as it reaches that point, 
or a little above it, a new grain structure is Vjorn that makes the metal 
more homogeneous. This formation of grain continues, after the steel 
leaves the press, until it has cooled below its lowest recalescent point, at 
which point it sets, and no more change will take place until it is reheated 
to the recalescence point. These two points occur in most steels at about 
1650° and 1400° F., but some of the special alloys show a wide variation 
from this. 

Thus it will be seen that if a forging is finished while it is too hot, 
the grain will be coarse and crystalline and the metal will not have the 
cohesive force that it should, and therefore the piece will not be as strong 
as a forging should be. On the other hand, if it is hammered, or squeezed, 
in a forging press after it has become too cold, the crystals will be crushed 
and the resiilt will be the same, but if it is forged at the proper heat, the 
grain will be fine, dense, and homogeneous, and the cohesive force will 
be greater than it was in the metal before it was forged. This will natu- 
rally increase the tensile strength and elastic limit. 

Many poor forgings are turned out by raising the temperature of the 
metal too suddenly. Certain molecular changes take place in the heating 
of all steels, and of the alloy steels in particular, which are liable to cause 
fissures in the core of the metal. These may not show in the finished 
product as they do not always break through the skin or outer shell of 
the forging. Thus, by heating suddenly, the outer shell becomes red 
before the core has had an opportunity to absorb any heat, and the outer 
shell expands, causing great strains on the core of the piece. In the 
case of a high percentage of nickel these fissures become more pronounced 
than with the other alloys. 

At a temperature of about 600° F., or a bright blue, most steels lose their 
ductility, and are not fitted to resist strains imposed upon them by the 
differential expansion of an unevenly heated metal. Therefore the rise in 
temperature from the normal to 600° should be a gradual one, but after 
this it may be brought up to the forging heat as quickly as is desired. 

To remove the internal strains caused by working the metal, all forg- 
ings, no matter how they are made, should be annealed before using, as 
the shocks to which the forging may be submitted will concentrate at 
the point where these intei-nal strains are the strongest, causing it to 
break at that point. The results are very similar to the machinist notch- 
ing a bar in order to break it. The heat treatment that is given the pieces 
after they are forged is an important factor, if the greatest strength and 
the best wearing qualities are to be given the metal, as the best forgings 
can be ruined by improperly heat-treating them afterward. 

Small forgings are usually tumbled, and large ones pickled in a diluted 



126 COMPOSITION AND HEAT-TREATMENT OF STEEL 

solution of sulphuric acid to remove the hard outer skin or scale that 
the finished forgings have. This is done so they can be machined more 
easily, as this skin or scale has a mineral hardness that cutting tools will 
not cut without becoming dull. 

Forgings that are made with a knowledge of metals, temperatures, 
etc., and with the proper skill and care, are stronger, and will stand the 
strains and stresses that are put upon them much better than the same 
steel when formed into shape in any other way, unless it be the rolled 
stock, which should be worked under the same temperatures. 

HAND FORGING 

When small pieces and but few of a kind are wanted, the hand forging 
is undoubtedly the cheapest; but for large pieces, or where a large quan- 
tity is wanted, hand forging is the most expensive way of producing them 
and the strength is not apt to be as great as by any of the other methods. 
With a blacksmith shop properly equipped, a skilled smith can make 
forgings that are stronger than a rolled bar from the same ingot. To 
do this the piece must be hammered between the proper temperatures, 
which varies with the different grades of steel. 

The steel that is the best adapted for forging under the hanmier has 
about the following composition: carbon, 0.15%; silicon, 0.20%; man- 
ganese, 0.52%; phosphorus, 0.06%; sulphur, 0.04%. This steel in the 
annealed state will show the following physical characteristics: tensile 
strength, 55,000 pounds per square inch; elastic limit, 30,000 pounds per 
square inch; elongation in 8 inches, 29%; reduction of area, 60%. When 
fractured it will show a silky fiber. 

But for many purposes a steel of much greater strength than this 
must be hand-forged and then it becomes necessary for the smith to 
understand the nature of its com.ponent parts so he can forge it success- 
fully, as many of the high-grade alloy steels can be rendered no better 
or stronger than the ordinary carbon steels by over or under heating 
and poor workmanship. 

In many cases welds are absolutely necessary to produce the required 
shapes, and a steel of the following composition is the best suitable for 
welding: carbon, 0.080%; silicon, 0.035%; manganese, 0.110%; phos- 
phorus, 0.012%; sulphur, 0.007%. In the annealed state it should show 
the following physical characteristics: tensile strength, 48,000 pounds 
per square inch; elastic limit, 25,000 pounds per scjuare inch; elongation 
in 2 inches, 27%; reduction of area. 



STEAM-HAMMER FORGING 



For pieces of considerable size and bulk the steam-hammer is sub- 
stituted for the hand-forging process. These hammers vary in size, 



WORKING STEEL INTO SHAPE 



127 



from the small Bradley cushioned hammer that strikes a blow of about 
500 pounds, as shown in Fig. 55, to those that strike a blow of many 
tons, as illustrated by Fig. 56, which is that of an 8-ton hammer, in use 
at the Bethlehem Steel Works. While this is not the largest hammer in 
use, it is about as large as is practical, owing to the inability of building 
a foundation that will prevent buildings near it from being wrecked, 
and other machine foundations ruined. Another style of steam hammer 
is shown in Fig. 57. This, however, is usually used for drop forgings. 

In this method of forging, the hammer should be of a size to suit the 
size of the work. The hammer-man must exercise a good deal of skill 
and judgment as to the power and speed of the blows delivered to the 




Fig. 55. — Bradley cushioned hammer. 



piece, as a too powerful blow will crush it, and in the case of a high per- 
centage of nickel, fissures and cracks are liable to develop which it will 
be difficult to get out, and which may show in the finished product. 

This is especially triie if the piece is allowed to fall below the forging 
temperature, or if the blows are not distributed evenly. If the blows are 
from a light trip-hammer, delivered at high speed, only the surface of 
the metal will be bruised and the core not affected, thus causing the core 
to be coarse-grained without the proper cohesion to insure the necessary 
strength. 

A heavy hammer, descending at a slow speed on work that is held at 
the proper temperature, will penetrate the mass to the center and 
allow the particles of metal to flow to their proper position and insure 
a fine grain of even texture and be uniform throughout its entire size. 

The keeping of the heat to a good forging temperature is more difficult 



128 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



than in the hand-forgings, owing chiefly to the difference in the size of 
the piece forged, as the hand-forged piece is usually small enough for 
the smith to put in the fire and reheat the minute the temperature falls 
below the best forging heat. But the hammer-forged piece is many times 
large enough to be handled with a crane, and is therefore liable to be kept 
under the hammer as long as a blow will have any effect on it. 




Fig. 56. — Steam forging hammer, 8-tou. 

This results in a very uneven structure, as when the metal is hot the 
blows will penetrate to the center, and as it cools they have less and less 
penetration until only the skin is affected, and the annealing, which is 
resorted to afterward, cannot bring it back to the proper homogeneity, 
as some parts will have a denser grain than others, and therefore be 
stronger. 



WORKING STEEL INTO SHAPE 



129 



The effect on the metal when the blows are not powerful enough to 
penetrate to the center, or the steel is not hot enough to allow them to 
do so, is shown in Figs. 58 and 59. When too. light a hammer is used, 
the effect shown in Fig. 60 is usually obtained. These same effects are 
often encountered in drop forgings and hand forgings, as well as in steam- 
hammer forgings. They are generally overcome by the use of a hydraulic 




Fig. 57. — Erie steam hammer. 



forging press, as with the press the metal is squeezed and consequently 
must be hot enough to flow into shape, and this affects it clear to the center. 



DROP-HAMMER FORGING 

When enough pieces, of one shape, are wanted to warrant making a 
set of dies, the cheapest and best way of producing these in either the com- 
mon carbon or high-grade alloy steels is by the drop-forging process. They 
can then be made in one piece without welds, except in pieces which are 
many times longer than a section through them, and these are so difficult 



130 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



to keep at the proper temperature that they are usually forged in two 
or more pieces and then electrically welded together. The oxy-acetylene 




Fig. 58. — Effect of hammer forging. 

blowpipe has been brought into use for welds of this character, as well 
as all other forms of welding, and good results are also being obtained 
in that way. 




Fig. 59. — Another sample of hammer forging. 

A good illustration of this is the front axle of an automobile, which 
is usually forged in I-beam section, 4 inches from the top to the bottom 
of the I, 2| inches across the flange, with the web J of an inch thick, and 



WORKING STEEL INTO SHAPE 



131 



a length of from 48 to 54 inches. These are generally forged in two halves 
and electrically welded in the center, but a few of them are forged in one 
piece, although the first cost of the dies and the liability of their breaking, 
owing to the axle cooling before the forging operation is completed, has 
made this method very expensive. 

The dies that are necessary for this kind of forging are usually made 
of a 60-point carbon steel and in two halves: an upper and a lower one. 
They are generally parted on the center line; but the shape of the piece 
controls the location of the parting line. The upper half of the die is 
fastened to a ram that is connected to the piston in a steam cylinder, 
and this is used as a hammer to strike the hot steel, held over the lower 
half of the die, a series of blows. This forces the metal to fill both halves 
of the die, and thus the piece is formed into shape. Dropping the upper 
half die onto the lower with a hammer-like blow has given this kind of 
forging the name of drop forgings. 




Fig. 60. — Piece forged with relatively light hammer. 



The dies are always given from 5° to 7° draft, so the forging will fall 
out easily, and they are left open on the parting line from | to i of an 
inch, according to the amount of metal in the forging. The amount of 
stock is always greater than in the finished forging, so it will completely 
fill the die, and the surplus is squeezed out at the opening on the parting 
line. This fin is afterward trimmed off. With hard or brittle steels it 
is best to make the dies with shorter steps between the different pairs 
than for the ordinary carbon steels. 

One of the first and most important points in die forging is the setting 
of the dies, as the upper half, which is fastened to the ram, and the lower 
half, which is fastened to the anvil block, must come exactly in line to 
produce a perfect forging. 

The lower half of the die should have a current of air blowing in it 
that is strong enough to remove all of the scale that works off from the 



132 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



piece being forged. The air blast should be directed so it will not cool 
the hot metal while being forged. Steel-wire brushes can be used for 
this purpose, but the air is quicker, and if well adjusted is more positive. 
The upper half of the die should be kept well oiled so the scale will not 
stick to that. This can be done by rubbing a swab, well soaked in oil, 
through the die every time it is raised off the work. 

With the dies pi-operly set and the press adjusted so the two dies will 
come together on the parting line, the work can be turned out to one 
thirty-second of an inch of the finished size, thus making much less machine 




Fig. 61. — Different operations on forging a crank-shaft. 

work than by the hand or steam-hammer forging processes, and when 
grinding is to be used in finishing, the work can be brought to within one 
one-hundredth of an inch. 

The cost of drop forgings depends on the number needed, and the num- 
ber that can be turned out at one setting of the dies, as well as on the 
quality of the steel used. 

Some of the largest pieces that are being made by drop forging are 
the crank-shafts for internal combustion engines, and the different opera- 
tions in forging these are shown in Fig. 61. At .4 is shown the straight 
bar, cut to the proper length. This is first bent to the shape shown at 
B in the bending press. It is then drop-forged, and when it leaves the 
dies, it is similar to the piece shown at C. The dies are usually left \ 



WORKING STEEL INTO SHAPE 



133 



inch apart on the parting line for this size of forging, to allow the excess 
metal to squeeze out between them, which forms into the fin that is shown 
at C. This necessitates the making of an extra pair of dies for shearing 
off the fins. After this is done the crank has the appearance of that 
shown at D. On this particular shaft there was a comparatively large 
flange on one end, as shown in E. This would be difficult to form in 
the dies when forging the rest of the shaft, and for this reason an extra 
amount of metal is left on the shaft at this point and the flange is formed 




Fig. 62. — Taking crank-shaft from furnace to hammer for first operation. 

in another set of dies after the rest of it has been forged. This com- 
pletes the forging operations and the shaft is ready to be machined; the 
machined crank-shaft being shown at F. 

One of the largest drop forgings that has so far been made (June, 1910) 
is a two-throw crank-shaft, made by the Bethlehem Steel Company, that 
when finished weighs 400 pounds. The operations are similar to those 
shown in Fig. 61. Fig. 62 shows the piece, after it has been bent and 
heated, as it is being taken from the furnace to the 5000-pound drop- 
hammer for the first operation. Back of the furnace can be seen the top 
of the bending press, which bends the straight bar to the shape shown by 



134 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



the partially forged crank in Fig. 64. Fig. 63 shows the piece being held 
under the hammer ready to drop the die on it. Fig. 64 shows the crank- 
shaft after it has been partly formed and as it is being taken back to the 
furnace to be reheated for the final forging operation under the hammer. 
Fig. 65 shows the crank-shaft as it was being taken out of the dies after 




Fig. 63. — 400-pound crank-shaft under hammer ready to drop the die. 



the final forming operation. In front of the hammer is shown a finished 
crank-shaft with a 5-foot rule standing beside it to show its length. 

An idea of the varietj^ of shapes, sizes, and styles of machine parts 
that can be economically made by the drop-forging process can be obtained 
from Fig. 66. At the lower edge of the half-tone is laid a 5-foot folding 
rule, and just above it is the 400-pound crank-shaft that has just been 



WORKING STEEL INTO SHAPE 



135 



described in its forging operations; while at the top of the picture are 
forgings that will require about twenty to weigh one pound. 



PRESSED FORGINGS 



The inferior quality of many die forgings is undoubtedly due to the 
drop-hammer process, as this has a tendency to produce only a bruising 




Fig. 64. — Removing partially forged 400-pound crank-shaft. 

effect, owing to the top die descending at a high speed and delivering a 
light blow which has no penetration. The hydraulic, pneumatic or steam 
press, on the other hand, produces forgings of a far superior quality because 
it slowly squeezes the metal into the shape of the die, thus allowing it 
more time to flow into place and assume its new shape, and therefore 



136 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



making it more uniform in quality with a great deal lower degree of internal 
strains. 

With the hammer blow in forging a wavy grain is obtained, as shown 
in Figs. 58 and 59, i.e., directly under each blow of the hammer a dense 
grain is produced, while around the edge of the blow it is less dense. This 
causes the ridges shown in the fracture of the fine-grained metal around 
the outside of the bar. In conjunction with this is the inability of the 
blow to penetrate to the center. In one or two places, where one blow 
did not overlap another, the shape of the metal affected by the blow can be 
plainly traced. Where the steel is pressed or squeezed into shape this 




Fig. 65. — Final forging operation. 

variation in the density of the grain of the piece would not show, and it 
would be condensed clear to the center, if the work was done properly, as 
the steel being operated on would have to be hot enough to flow into the 
shape desired under the high pressure used, or it could not be worked. 

That the press makes a more homogeneous metal than the hammer, 
or even the rolls, and hence a stronger and tougher one, is well illustrated 
by the German government specifications for steel forgings worked by 
rolls, hammer, or press which says: "Forgings made from rolled or 
hammered steel must have the initial section at least eight times that of 
the finished section; while those made from pressed steel need have an 
initial section only four times the finished section." 



WORKING STEEL INTO SHAPE 



137 




138 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



With the press, rounds, fiats, squares, and irregular shapes can be 
forged without dies, as with the steam hammer, or two halves of a die 
can be pressed together to make die forgings, the same as with the drop 
hammer. When forging metal into shape, a much greater force can be 
brought against it, with the press, than with the hammer, owing to the 




A 1400-ton forging press. 



absence of any jarring. As a consequence of this the steel works are all 
adopting presses for their biggest work. Some of these operate at a very 
high speed, when compared with the hydraulic presses of a few years 
back. 

The power behind the press is obtained by the use of either water, 
air, or steam, but the hydraulic press is the one that has been almost 
universally adopted. A large-sized press of this kind is shown in Fig. 67. 



WORKING STEEL INTO SHAPE 



139 



This is a 14,000-ton press at work on a forging, but it is typical of the 
style of hydraulic presses, and they can be obtained in much smaller sizes. 




Fig. 68. — Small high-speed steam-hydraulic forging press. 

In place of the upper and lower press blocks used, others can be inserted 
that will form rounds, octagons, etc., or the two halves of a die can be 
put in their place to form irregular shaped pieces. 



140 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



A combination of the steam-hammer and hydrauHc press has recently 
been placed on the market, and this promises to have a very useful field. 




Fig. 69. — Large high-speed steam hydraulic forging press. 



One of the smaller sizes, with a single frame, that is built in sizes from 
150 to 400 tons, is shown in Fig. 68, and a large size with four columns, in 
sizes from 300 to 12,000 tons, is shown in Fig. 69. These machines raise the 



WORKING STEEL INTO SHAPE 



141 



ram and lower it onto the work, which can be done with a blow if desired, 
and then the water pressure is turned on to squeeze the piece into shape. 
It also can be used with or without finished dies in the making of forgings. 

With the hydraulic press it is possible to make simple, inexpensive 
dies that will forge quite complicated pieces. Pieces that are impossible 
to make in the drop-hammer and are very expensive to make by hand- 
forging can be made remarkably cheap and accurate. As an example 
of this, the piece shown in Fig. 70, after the machine work was done, was 
forged in a hydraulic press with the apparatus described below. 







y The Cone on Hub 

/ taper3 14" per Foyt. 



Fig. 70. — Wheel hub to be forged in hy- 
draulic press. 

A piece of 3§-inch round stock was cut the required length and put 
in the die, as shown at G in Fig. 71. Here, A is the die-holder; C the die 
block, which is put in loose, and E the flanging punch. A loose block 
is put under the piece G and when it leaves the press it is the shape 
shown in Fig. 72. The next operation is to punch out the center and 
spread out the top to form the shoulder, and this is shown in Fig. 73. 
Here the die in Fig. 71 has had the loose block in the bottom taken out, 
and the two halves of the die block, D, B (Fig. 73), placed on top of the 
forging. When the punch is pressed down it forms the piece into the 
shape shown in Fig. 74, and when the bottom of this is trimmed off it 
leaves i of an inch finish all over. 



142 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Thus, while the press makes forgings with much better metal than those 
turned out with any kind of a hammer, it also presents greater possibili- 



Top Platen of Press 



Punch Bolder 




Bottom Platen of Press 



Fig. 71. — -Stock in die ready for first 
operation. 

ties to the maker and user of forgings in the way of difficult shapes that 
can be economically made. The example given is merely one of a large 
variety of shapes that can be made in a similar way with the use of loose 




Fig. 72. — Cross-section of forging after 
first operation. 

dies. Fig. 75 shows a few more shapes that have been made in the 
hydraulic press; some of which were made with loose die blocks, and these 
will doubtless suggest to the student many more that can be made. 



WORKING STEEL INTO SHAPE 

Top Platen of Press 



143 



Die in Two Parts so that 
/ it can be removed from 

Forging. 




Forging be for© 

-nd Operation. 



Bottom Platen of Press 



Fig. 73. — Forging in die ready for second 
operation. 



BeceB3 is formed by 
large Siioulder on Punch F 




The Part below Une la 
Cut off leaving a Forging 
with a Hole directly 
through it. 



Fig. 74. — Forging after second operation, 
ready for machine shop. 



144 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Welding 

In many of the more intricate shapes that are hand-forged, a resource 
is had to welding, and if the average smith were told that he could not 
make a perfect weld he would feel greatly insulted. But from a large 
number of so-called perfect welds that were examined very few showed 
a strength equal to 50% of the unwelded section. With the alloy steels 
it is difficult to get a weld that will even show that percentage, as nickel, 
chromium, vanadium, tungsten, aluminum, and some other alloys do 
not lend themselves to the welding process. It is difficult to make 
welds at all by the hand methods in a blacksmith's forge, when these 




tttMAm mA 

Fig. 75. — More shapes made in hydraulic press with loose die blocks. 

are ingredients of the steel to be welded. Some of these steels have been 
welded, but an efficiency of over 2-5% is seldom obtained. 

Carbon, however, is the principal enemy of welds, and with this as 
low as 0.15% it must be handled with great care at the welding heat, 
while with 0.20% of carbon the steel is very unreliable, and with 0.50% 
of carbon the steel is liable to be burnt at a temperature well below the 
welding heat. 

Thus to make hand-forgings where welds are necessary, the pieces 
must be from two to three times the size of that necessary for the required 
strength, and with some of the alloyed steels even this will not suffice. 



PRINCIPLES INVOLVED 



Welding consists of heating two pieces to a high temperature, then 
dissolving off the iron oxide, which has formed on the surface, by the use 



WORKING STEEL INTO SHAPE 145 

of some flux, such as borax, and then firmly pressing the pieces together. 
Welding plates are sometimes put between the pieces to be welded in 
place of the borax. These are special preparations which are made for 
this purpose, and are covered by patents. 

The exact temperature at which to heat pieces for welding is not known, 
but it is near the melting point, as the steel must be in a soft, almost 
pasty, condition. The pieces are usually upset or enlarged at the ends, 
so that the section at the weld will be larger than the rest of the piece. 
In the ordinary weld they are hammered continuously until the metal has 
cooled to a dull red. This breaks up the coarse crystals which have been 
produced by the high temperature, and by finishing at a low temperature 
^a small grain is secured. 

This small grain is obtained, in the metal close to the weld, by proper 
welding, but there is always a place within a short distance of the weld 
that must have been heated to the high temperature, which means 
overheated, and has not received the mechanical treatment given at the 
weld by hammering it down to the proper finishing temperature. This 
will cause the metal to have a coarse grain at this point, which is usually 
from 4 to 8 inches from the weld, and the steel to bi'eak when submitted 
to a strain much less than the original strength of the metal welded. Thus, 
while the average welder may say that if no break occurs at the weld 
it is as strong as the original piece, this is not true and welds are seldom 
made by hand methods that have more than 60% of the efficiency of 
the original piece. In a large number of tests which were made it was 
found that the cause of damage was the bad crystallization adjacent to 
the weld. 

All steels that have been welded would give better results if they 
were reheated to a little above 1650° F., as this heating would restore 
to a large extent the grain size of all parts. 

Steel is overheated when the first drops of melted metal begin to form 
in the interior of the mass. These segregate to the joints between the 
crystals and cause weakness. The second stage of this is when the molten 
drops segregate as far as the exterior and leave behind a cavity filled 
with gas. The third and last stage is reached when gas collects in the 
interior under sufficient pressure to form miniature volcanoes and break 
through the skin. This projects liquid steel and produces the well-known 
scintillating effect of this temperature. Into the openings formed by 
these miniature explosions air enters and oxidizes the interior. Mechan- 
ical pressure applied to the steel, such as squeezing, hammering, etc., 
if carried on continuously until the metal has cooled to a dull red, will 
bring the steel back to its original condition and grain. By reheating 
to a little above 1650° F., after the piece has been welded, will also aid 
in restoring it to its original condition. 



146 COMPOSITION AND HEAT-TREATMENT OF STEEL 



ELECTRIC WELDING 

The hand method of welding being a slow, laborious process when 
large pieces were to be welded, and the efficiency of the welds being low, 
it became necessary to abandon welding, in many cases, as a commercial 
possibility, or to invent some other means of performing the welding 
operation. This necessity brought into use two electrical welding processes 
and several gas processes. 

In the electrical resistance process the pieces to be welded are usually 
butted together and clamped so there will be a pressure against each other. 
Two electrodes are then placed on each side of the joint to be welded, and 
the current of electricity passing through these also passes through the 
steel at the joint. This softens the metal by heating it nearly to the 
melting point, and the pressure of one piece against the other squeezes 
them together until they are welded. 

This process has many advantages over the hand method. The 
heating can be localized and held in the immediate vicinity of the weld, 
and the hand can be held on the metal but a very few inches back from 
the weld. This prevents the metal from crystallizing 6 or 8 inches back 
as in the forge-heated piece; the temperature of the surfaces to be welded 
is always under control, which reduces the danger of overheating the 
steel to a minimum. The pressure between the abutted pieces may 
be regulated to any pressure desired and very irregular shapes may be 
butted together and welded in a very accurate manner. The efficiency 
of the weld has been increased 50%, and in some cases 100% over that 
of hand welding. 

The other electric welding process is called arc welding. In this a 
carbon electrode is placed in a holder so it can be held in the hand close 
to the work, which is placed on an iron or steel-topped table. This table 
is connected to a rheostat, and that to the power supply, as is also the 
carbon electrode. A water rheostat is usually used. With the proper- 
connections made, the electric current flows through the rheostat and the 
carbon electrode and strikes an electric arc, the same as do the arc lamps 
seen in the street. This creates an intense heat that melts the metal 
on each side of the joint, and by holding a rod in the other hand, new 
metal can be fused with the old metal in the joint, and the two pieces 
stuck together. 

This is a process of casting steel into the joint, and hence rolled or 
forged metal cannot be made as strong as the original stock except by 
leaving a ridge at the weld, so the metal will be thicker. Even this, 
however, will make a stronger weld than can be made by the blacksmith 
with a hammer, anvil, and forge fire. If the arc electric welds were ham- 
mered after welding, while the metal was still hot, and before it had cooled 



WORKING STEEL INTO SHAPE 147 

to a dull red, the weld could be made much stronger, as this would change 
the grain from the coarse crystalline one of a casting to the more dense 
grain that approaches that of a forging. 

Alloyed steels that do not lend themselves readily to welding by hand 
can be successfully welded by the electrical process. The density of the 
metal is much more uniform when welded by electricity than by the hand 
method, and the weld is made in a fraction of the time. The amount 
of work required in finishing after electric welds is very small, as it leaves 
it comparatively smooth; a slight ridge right at the weld being practically 
all the deformation there is in the metal. 

This has aided greatly in the production of forgings, as they can be 
made in two, three, or more pieces and afterward welded together. It 
has also been found in many cases to be a better method than brazing, and 
in such cases is used in place of it. 

WELDING WITH GASES 

Several different processes of welding with gases and a blowpipe 
or torch have recently been developed, and these have become quite a 
factor in the manufacture and repair of metal parts of all kinds. The 
gases used for these various processes are oxygen, acetylene, hydrogen, 
liquid gas, city gas, and natural gas, and most of them use two of these 
gases in combination. All of these processes operate in the same way 
as the arc electric; i.e., they melt new metal into the joint and fuse it with 
the old. 

Of the several gas processes the oxyacetylene has taken the lead, 
and this consists of heating the metal with a torch, using oxygen and 
acetylene gas. With this the metal is heated to the melting point, and 
a steel rod is passed along with the flame, when steel is being welded, 
and the metal melts off from the rod and flows into the joint until it has 
been filled. 

The flame is largely carbon monoxide, but at the tip where the heating 
takes place it is converted into carbon dioxide. This gives a flame that 
will neither carbonize or oxidize the metal. In lighting the blowpipe 
or torch the acetylene is first turned on full, then the oxygen is added 
until the flame has only a single cone whose apex has a temperature of 
about 6300° F. Too much acetylene produces two cones and a white 
color, while an excess of oxygen is shown by the flame assuming a violet 
tint and a ragged end. The best welding results are obtainable with 
1.7 volumes of oxygen to one of acetylene. 

The oxygen for the process is obtained by either using a special gen- 
erator that generates oxygen from chemicals, or by buying the oxygen 
that is stored in steel bottles and sold in the open market. It is used 
at a pressure of about 15 pounds per square inch. The acetylene gas 



148 COMPOSITION AND HEAT-TREATMENT OF STEEL 

is manufactured in the ordinary way from calcium carbide, and used at 
a pressure of 2 or 3 pounds. 

Through a system of piping, the flame is easily carried to the work, 
which saves the labor of moving large pieces of work to a forge or hammer 
for welding. Pieces one inch thick have been successfully welded with 
this process, but its best application is in welding thinner sheet metal, 
as joints of great length can be easily welded. In fact, its only limit is 
the length of the joint and the time needed, and this latter can be carried 
out indefinitely. 

Oxy acetylene welding gives its best results in the welding of steel, 
but cast iron is being welded successfully as well as copper, brass, and 
bronze. 

The different metals can also be welded together as is shown in Fig. 




Fig. 76. — Steel, copper, brass, and bronze welded ogether. 

76, in which four plates were butted together and welded. One plate 
was steel, as shown by the white square; another brass, as shown 
by the darker square in the diagonally opposite corner; and the two 
very dark squares were copper and bronze respectively. After welding 
these they were bent and broken at the joints to see if they were 
thoroughly welded, and from the appearance of the fractures they would 
indicate a perfect weld. The steel welded to the copper and bronze as 
well as the brass did. Owing to the high heat of the flame, however, 
some of the lead and zinc in the brass and bronze melted out, leaving 
holes in the metal. 

This welding process, as well as all the other gas processes, makes the 
weld by casting metal into the joint in the same way as does the arc elec- 
tric welding process. Therefore, on rolled or forged metal the joint is 
not as strong as the original metal, but it is stronger than a weld made 



WORKING STEEL INTO SHAPE 149 

with a forge fire, hammer and anvil, and metals can be welded that 
it is impossible to weld in the latter way. In some cases an efficiency 
of 90% has been claimed, but if the work is properly done an efficiency of 
at least 80% can be obtained with any metal. 

The oxyhydrogen process only differs from the oxyacetylene in that 
hydrogen gas replaces the acetylene gas. The oxygen and hydrogen are 
used in the proportion of from 2 to 4 parts hydrogen to 1 of oxygen, and 
the hottest part of this flame is about | of an inch from the point of the 
burner. 

Two parts hydrogen to one of oxygen will give a flame with a temper- 
ature of about 4350° F., but if a flame is desired with a reducing action 
it is necessary to use 4 parts of hydrogen to 1 of oxygen, and this will 
have a temperature of about 3450° F. This flame will melt iron or steel, 
and cause it to weld even if the surfaces are not clean, as any rust present 
will be reduced. It is also a very good flame to use for the cutting up 
of metals. This lower temperature of the flame is really better for 
sheets up to J of an inch thick, as the melting of the metal is less rapid 
and less explosive, giving a welded joint that is cleaner and with fewer 
scars and blisters. 

The oxyliquid gas welding process consists of replacing the acetylene 
or hydrogen with liquid gas, and as this combination generates a heat 
of about 4000° F., it will make welds that are equal to either of the 
above processes, and for all practical purposes it is as good. The 
liquid gas is a product that is made from crude oil and stored in steel 
bottles, similar to oxygen, at a high pressure. At this pressure it is a 
liquid, but when allowed to expand to the 15 pounds pressure required 
for welding, it becomes a gas, and is mixed with the oxygen in a torch, 
the same as the other processes. 

Another process uses city or natural gas and oxygen. These are 
combined in a torch, to get the proper mixture and generate the neces- 
sary heat for welding. For many purposes this is very useful, but the 
flame does not have as high a temperature as the others. 

Still another process consists of combining city or natural gas with 
two blasts of air; one of which has a high pressure and the other a low 
pressure. These are sent through a special torch and have been used to 
successfully weld cast iron and the non-ferrous metals. It does not 
seem to develop enough heat to weld steel, and therefore its field seems 
to be limited to metals of a lower fusing temperature than steel. Acety- 
lene has also been used in addition to the above gas and air with good 
results. 

THERMIT WELDING 

The thermit process of welding is radically different from all the other 
processes, and is useful for an entirely dift'erent class of work. 



150 COMPOSITION AND HEAT-TREATMENT OF STEEL 

With this process, a sand mold is built around the pieces to be welded 
and the metal poured in this. The mold is made of sand and clay, which 
should be mixed thoroughly stiff and as dry as possible, as the less mois- 
ture there is in the mold the better will be the results obtained. For 
this reason the mold should be dried in a furnace or oven at a low tem- 
perature for from six to eight hours. To test the dryness of the mold, 
two or three wires can be rammed up in the thickest section of it and these 
pulled out after drying to see if any moisture remains. 

With the mold completed the thermit is placed in a special receptacle 
which is located over the mold. The thermit consists of aluminum and 
oxide of iron. A little magnesium is placed in this and lighted with a 
match which immediately sets up a tremendous chemical action, which 
produces a superheated liquid steel and superheated liquid slag that 
is aluminum oxide. When the mass is entirely molten it attains a tem- 
perature of 5400° F. The bottom of the receptacle is then tapped and 
the liquid metal runs into the mold and into and around the joint to 
be welded. The high temperature of the liquid mass causes the ends 
of the pieces to be welded, to become molten and pasty, and fuse with 
the thermit. 

Welds were made with this process on a bar of rolled steel, 2 by 4i 
inches, which was broken, then welded, and afterwards tested. The tests 
showed an efficiency of 97% in tensile strength and 88% in elastic limit. 

The greatest usefulness of this method of welding is for the stern frames 
of steamships which have broken, locomotive side frames, driving wheels, 
connecting rods, and other things of a similar nature, but the building 
of the mold makes it commercially prohibitive where autogeneous or 
electric welding can be used economically. 



CHAPTER VIII 

Furnaces and Fuels Used for Heat-Treatment 

In working steels it is very important that they be properly heat- 
treated, as poor workmanship in this regard will produce working parts 
that are not good even though the stock used be the highest grade of 
steel that is procurable. And by improperly heat-treating them it is 
possible to make high-grade steels more brittle and less able to support 
a load or withstand stresses than ordinary carbon steels. All steels are 
improved in tensile strength, elastic limit, elongation, or reduction of 
area by annealing, hardening, or tempering them. The different treat- 
ments are divided into three distinct classes, the first of which is harden- 
ing, the second annealing and reheating, and the third case-hardening, 
carbonizing, or cementing. 

The theory of heat-treatment rests upon the influence of the rate of 
cooling on certain molecular changes in structure occurring at different 
temperatures in the solid state. These changes are of two classes, critical 
and progressive; the former occur periodically between certain narrow 
temperature limits, while the latter proceed gradually with the rise in 
temperature, each change producing alterations in the physical charac- 
teristics. By controlling the rate of cooling, these changes can be given 
a permanent set, and the physical characteristics can thus be made differ- 
ent from those in the metal in its normal state. 

The results obtained are influenced by certain factors as follows: 
First, the original chemical and physical properties of the metal. Second, 
the composition of the gases and other substances which come in con- 
tact with the metal in heating and cooling. Third, the time in which the 
temperature is raised between certain degrees, or the temperature-rise 
curve. Fourth, the highest temperature attained. Fifth, the length 
of time the metal is maintained at the highest temperature. Sixth, the 
time consumed in allowing the temperature to fall to atmospheric or 
the temperature-drop curve. 

The third and sixth are influenced by the size and shape of the piece; 
by the difference in temperature between it and the heating and cooling 
mediums, and by the thermal capacity and conductivity of the latter. 
Each of these may vary widely within the temperature range to which 
the piece will be subjected. 

151 



152 COMPOSITION AND HEAT-TREATMENT OF STEEL 

The first, second, third, and fourth are but elements of the heating 
process, and the sixth of the cooling. The method of heating the alloy- 
steels is very important, as mechanical injuries are liable to occur, in 
the external layers of the metal as well as the internal, from a too rapid 
rise in the temperature, especially at the start. 

The highest temperature that it is safe to submit a steel to for heat- 
treating is governed by the chemical composition of the steel, and this 
temperature should be about 40° F. above the highest point of trans- 
formation in the steel considered. Thus pure carbon steel should be 
raised to from 1450° to 1650° F., according to the carbon content, 
while some of the high-grade alloy steels may safely be raised to 
1750° F., and the high-speed steels may be raised to just below the 
melting point. It is necessary to raise the metal to these points so that 
the active cooling process will have the desired effect of checking the 
crystallization of the structure. If raised above these temperatures, in 
an oxidizing atmosphere, the surface of the piece becomes covered with 
a scale of iron oxide and oxidation extends to the elements combined 
with the iron. 

When these oxides remain within the metal, they tend to form a film 
of separation between the metallic grains, thus destroying the cohesion 
between them, and the metal is said to be burned. After burning, it 
cannot be brought back to its former strength without remelting. If 
the temperature is maintained within the crystallogenic zone, disaggre- 
gation proceeds, so that the longer it is subjected to this temperature 
and the higher the temperature the less homogeneous it becomes and 
the coarser its grain after quenching. Steel in this state is called 
over-heated. It can be partially returned to its former strength by 
repeated forging when heated above the critical temperature, followed 
by positive quenching, or it may be restored by a proper method of 
heat-treating. 

When, as always happens, the grain has become coarsened by over- 
heating it must be refined again to bring it back to its original condition. 
To do this it is necessary to heat the metal to the point where a new crys- 
tal-size is born, as the coarsening of the grain is merely a growth of the 
crystals, and these crystals grow with every increase in the temperature 
above the point necessary for hardening or annealing. If we barely pass 
the degree of temperature at which this new crystal-size is born we will 
obtain the smallest grain size that the steel is capable of. This tem- 
perature varies with the carbon content of the steel. The higher the per- 
centage of carbon the lower the degree of temperature that will be required; 
a low-carbon steel must be heated to 1650° F., a 0.40% carbon steel 
to 1475° F., and so on. Some of the special alloying materials also affect 
this temperature as well as the size of the grain. 



FURNACES AND FUELS USED FOR HEAT TREATMENT 153 

FURNACES AND THEIR FUELS 

Owing to the nature of most steels they must be handled very care- 
fully in the processes of annealing, hardening, and tempering; for this 
reason much special apparatus has been installed in the past few years 
to aid in performing these operations with definite results. This appa- 
ratus is divided into two distinct classes; that is, the apparatus for heating 
the metal, and that for cooling. In heating the metal four methods are 
used; namely, furnaces using solid fuel, liquid fuel, gaseous fuel, and elec- 
tricity. 

The forge fire was at first used for burning solid fuels, such as coal, 





1 



Fig. 77. — Hard fuel furnace for heat- 
treating steel. 



coke, charcoal, etc., to heat metals. From this developed the enclosed 
furnace, as shown in Fig. 77, and consequently these are the most numerous. 
In the furnace is a grate on which to burn the fuel, and over this an arch 
to reflect the heat back to a plate on which the work is placed. This 
plate should be placed so that the flames will not come in contact with 
the pieces of metal to be heat-treated. For this reason cast iron or clay 
retorts are sometimes used in the furnace to place the work in, while the 
necessary heat is obtained by the flames encircling these. They only 
have an opening on one side, and this is placed opposite the front door, 
so the work can be easily passed in and out. The oxidation, sulphura- 



154 COMPOSITION AND HEAT-TREATMENT OF STEEL 

tion, etc., that spoil the smooth surfaces of the work, and are largely 
caused by the product of combustion of the hard fuels, are thus eliminated 
as much as possible with this kind of furnace and fuel. With this furnace 
it is necessary to keep the heat in and the cold air out as much as pos- 
sible, and therefore the doors should open and close very quickly to aid 
in the rapid handling of the work. For this reason the sliding doors 
with counterbalancing weights, as shown, should be used. 

The disadvantage of this style of furnace is that it is almost impos- 
sible to keep a constant temperature, and as a chimney nmst be provided, 
much heat is lost through that. By not being able to keep a constant 
temperature, it is impossible to measure the heat with a pyrometer, and 
the heat must be judged entirely by the color, as seen with the eye, and 
this makes the results depend entirely on the skill and experience of the 
workman. Also the atmospheric air and gases generated by the combus- 
tibles or a combination of both come in contact with the hot metal. These 
are liable to cause the metal to lose some of its carbon content, especially 
at corners or on thin delicate sections, from the oxidizing influence of 
the oxygen in the air or other causes. The combustibles are also liable 
to contain injurious ingredients, such as sulphur, which are liable to 
enter the steel. 

LIQUID FUEL 

Furnaces that use a liquid for fuel, such as crude oil, kerosene, gaso- 
lene, naphtha, etc., are becoming more numerous every day, owing to 
the ease with which the fire is handled and their cleanliness over the coal, 
coke, or charcoal fire. 

Crude oil and kerosene are the fuels generally used in these furnaces, 
owing to their cheapness and the fact that they can be obtained nearly 
everywhere. The adoption of oil for fuel has resulted in a considerable 
saving in the fuel bill over that of the coal-burning furnaces, and has 
also made a big improvement in the cleanliness of the hardening room. 
In fact, where natural gas is not obtainable at about one-quarter of the 
price of city gas, crude oil is by far the cheapest fuel that can be obtained 
for heat-treating furnaces. An exception to this might be made in the 
future when considering producer gas, but at present enough data has 
not been obtained by which to draw comparisons. 

One of the simpler of these oil-burning furnaces is shown in Fig. 78. 
With any of the oil furnaces gas can be used as a fuel by merely changing 
the burners. With a properly designed furnace the temperature can 
be raised quickly to the point desired; can be maintained at this tem- 
perature for any length of time, and an even heat can be kept throughout 
the entire chamber of the furnace. With the proper fuels and valves 
for regulating this, the temperature in the furnace can be raised or 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



155 



lowered as rapidly or as slowly as necessary for the different kinds of 
work. In the annealing of metals also the rate of cooling can be made 
as slow as needed if the proper equipment is installed. All of this can 
be accomplished without the customary smoke, soot, ashes, dust, gases, 
and foul odors that are met with in hardening rooms where the old hard 
fuel furnaces are used. The saving in the time consumed by the oper- 
ator in running the furnace is also an important factor, as when the proper 
temperature is once obtained and the valves set, practically no time is 
required for this part of the work. 

The installation of the furnaces and their necessary equipment is very 
important for the proper operation of the same. For safety, it is best 
to have the fuel supply in a tank outside of the building and pipe it, under- 




FiG.78. — Oil-burning, annealing, tempering, 
and hardening furnace. 



neath the floor, to the furnace. As a blast of air is necessarj^, this can 
also be piped, under the floor, from the fan, blower, or air compressor. 
The air and fuel pressures must be steady, uniform, and voluminous 
enough to give the furnaces their proper temperature and maintain it 
at the point desired. This, of course, varies with the kinds of material 
to be heated. 

Where accurate temperature control is not necessary, and pressure 
under 14 ounces will suffice, the steel fan or positive blower, that 
will give the proper volume, will maintain a uniform pressure. Where 
pressures from 2 to 5 pounds are required the positive blower is needed, 
and when an air pressure above this is necessary the compressed-air plant 
will be needed. In some cases good dry steam will give better results 
at a high pressure and effect a saving in the fuel. In that case steam 



156 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



pipes take the place of the air pipes, and these connect up to the steam 
supply. To heat steel to a good red, 50 pounds oil pi-essure or 110 pounds 
steam pressure gives very good results. The quantity of fuel needed 
varies with the temperature required, material treated, and speed at which 
it is handled, but the fuel pressure must always be uniform. For the oil 
5 pounds pressure is sufficient. 




Fig. 79. — High-pressure oil burner. 



In some cases between the tank and furnace is located a coil of pipe 
through which the fuel flows and over which a stream of water is flowing 
to keep the liquid at a low, even temperature when it enters the burners, 
which are located in the furnace. 

The burner to be used is an important factor in economical produc- 
tion, and it is not practical to have one burner that will do all kinds of 



FUHNACES AND FUELS USED FOR HEAT-TREATMENT 



157 



work. Whether high or low pressure air or steam is to be used for the 
blast makes a difference in the kind of burner that should be used to 
get the greatest efficiency with the minimum fuel consumption, as well 
as the temperature that it is necessary to maintain in the forge, and the 
nature of the work that is to be done. In Fig. 79 is shown a good design 
of high-pressure oil burner. 




Fig. 80. — Details of construction of 
over-fired furnaces. 



The dial with the figures and the pointer at the bottom have been 
added for fine adjustment. The sectional view at the tip shows the method 
of controlling the volume of atomized oil that is injected into the furnace. 

With this fuel hardly any work is required to keep up the fires, as they 
can be lighted in the morning and the temperature regulated by the turn- 
ing of a few valves and cocks. A more even temperature can thus be 



158 COMPOSITION AND HEAT-TREATMENT OF STEEL 

kept in the furnace than with the solid fuels, but the opening of the doors 
to handle the work reduces the temperature of the furnace the same as 
with the solid fuels. The action of the gases of the combustibles, or 
the oxygen of the atmosphere, in attacking the hot metal gives the same 
disadvantages. 

The furnaces are built in the over-fired and the under-fired type. 
In the over-fired furnace, as shown in Figs. 80 and 81, the atomized gas 
from the oil burner is sent into an opening over the heating chamber 
that is separated from it by an arch. Here the gas is burned and passes 




Fig. 81. — Small over-fired furnace. 

through numerous openings in the arched roof of the heating chamber, 
as indicated by the arrows in the right-hand view in Fig. 80. The burned 
gases then pass out through holes in the side of the heating chamber, close 
to its floor; then under it and up through flues on the opposite side. 

Thus the entire heating chamber is uniformly filled with the products 
of combustion and the spent gases utilized to heat the floor of the working 
chamber. This gives a soft uniform heat throughout the working cham- 
ber, and the temperature is so easily raised, lowered, and controlled that 
overheating or burning the metal can only result from gross carelessness. 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 159 

This uniform heat in the heating chamber also reduces to a minimum 
the distortion and warping that results from uneven heating, and a more 
even hardness can be obtained throughout the piece than can be produced 
with a hard fuel or under-fired furnace. 

With the proper fuel supply and valves to control the same, the tem- 
perature of the heating chamber can be maintained for an indefinite 
period, within 25° F. of any temperature between 600° and 2000° F. 




Fig. 82. — Double-end furnace with tank for quenching bath attached. 



On test runs of 1| hours each, at certain temperatures, the variation was 
not over 10 degrees. 

For high-grade alloy steels, where the most accurate results are required, 
the muffle furnace should be used, as in this style the products of com- 
bustion directly attack the metal, and it is liable to absorb some impurities 
from the gases. These impurities might weaken the metal and leave it 
less liable to withstand the strains and stresses put upon it, than would 
be the case if the metal were protected from them. For ordinary work, 



160 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



however, the injury is so slight it can be overlooked, as the fuel consump- 
tion is much lower in this than in the muffle furnace. 

A furnace open at both ends, wth a tank attached to hold the quench- 
ing bath, is shown in Fig. 82. 




Cross SsctioD A-B. 



Fig. 83. — Details of under-fired furnace. 



In the under-fired furnace, as shown in Figs. 83 and 84, atomized gas 
is injected into an opening underneath the heating chamber, and there 
the combustion takes place. It then passes through flues into the top 
of the heating chamber, and out of here through openings near the floor 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 161 

into flues on the opposite side. These conduct it out of the furnace. 
The burners and the flues on this, as well as the over-fired furnace, are 
staggered on opposite sides of all the larger furnaces, to make the heat 
uniform in all parts of the heating chamber. 

The construction of this furnace is simpler, and hence its first cost 
is less than that of the over-fired type. It is also much easier to reline 
and repair when burned out. The fuel consumption, however, is slightly 
greater than in the over-fired type and a uniform heat in all parts of the 




Fig. 84. — Small under-fired furnace with complete 
oil-burning outfit. 



work chamber is not as easi!}^ obtained, especially in large furnaces. In 
the smaller under-fired furnace the heat is easily controlled, and with 
oil fuel a high temperature can be attained and maintained throughout 
the day. This makes it very useful for tool hardening and tempering. 

In Fig. 85 is shown an oil-burning furnace with a self-contained outfit 
that makes it portable, and Fig. 86 shows one with a water-cooled front. 
The latter is made of fire-brick, with any size or shape of openings desired, 
and is very useful for heating the ends of tools and keeping the bar cool 
enough to handle. In both of these furnaces a temperature of 2500° F. can 
easily be maintained, and thus any kind of high-speed steel can be hardened. 



162 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Another style of oil furnace is the muffle furnace. In this the gases 
surround the heating chamber, but do not enter it. Thus the metal is 
protected from any injurious effects from the gases of combustion while 
they are being heated. 

Any of the above liquid fuel furnaces can be used for the gaseous 
fuels by merely changing the burners. 




Fig. 85. — Portable oil furnace with self-contained 
outfit. 



GASEOUS FUEL 

Furnaces using gaseous fuel are growing in favor, and are constructed 
so they can use either natural gas, artificial gas, or producer gas. They 
are very easy to regulate, and if v/ell built are capable of maintaining a 
constant temperature within a wide range. Their first cost is greater 
than that of solid fuel furnaces. The cost of installation, however, is soon 
paid for where natural gas, or possibly producer gas, is used for fuel, as 
then it is the cheapest furnace to operate. Artificial or city gas is more 
expensive than oil for fuel, but is much cleaner and easier to operate, as 
it is not necessary to install tanks or apparatus in which to store the supply. 
If the cost of the upkeep of these be figured in, there might not be such 
a great difference in the cost of furnace fuel, providing the city gas be 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



163 



obtained at a reasonable price. Where high-grade steels are used, and the 
best work is demanded, doubtless gas is the best fuel. 

Producer gas is continually increasing in use for furnaces, but unless 
a number of furnaces are operated, or a few large ones, a separate pro- 
ducer plant to supply the furnaces is not economical. Where a producer 
plant can be utiUzed for other things, such as furnishing power, it is prob- 
ably a very cheap fuel to pipe from the central power plant and burn 
in the furnaces. With this, or any of the gas fuels, a large part of the 
heat that goes up the chimney, when other fuels are used, can be utilized 
in heating the air of combustion that enters the furnace. This can be 
done with very little special construction. 




Fig. 86. — Oil furnace with water-jacketed front. 

Results which are very uniform are obtained with the gas furnaces, 
and it is much easier to maintain a constant temperature for liquid 
baths than in a solid fuel furnace, or a metal retort may be used 
to place the work in for the purpose of keeping it away from the gases 
of combustion, with a greater assurance that the work in it will be 
raised to the proper temperature and maintained evenly for a given 
length of time. 

One of the muffle or oven style of furnaces that uses gas for fuel is 
shown in Fig. 87. In this the blast connects at C with the end of the 
drum D, and goes through the pipe A, where it picks up the gas at G 
and carries it to the burners B. In placing a cutter like X, in the furnace, 
it should be supported by a fire-brick similar to F, so the teeth will not 
touch the bottom slab Z. The door E has a counterweight above H, 



164 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



so it can be opened and closed quickly, and it slides in the guides S. At 
P is a peep-hole, and at F is a vent to allow the gases to escape from the 
furnace. This principle has been carried farther by revolving the oven, 




Fig. 87. — Gas furnace with oven. 



or work holder, and sending the heating gases around it, as shown in 
Fig. 88. 

Pyrometers can be used very easily to measure the heat with this 
style of furnace. Thus definite results may be obtained in the degree 
of temperature without depending on the skill or knowledge of the work- 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 165 

man to as great an extent as with the furnaces using coal, coke, or charcoal 
for fuel. Furnaces using liquid and gaseous fuels differ very little in 
their construction, and are made in many different styles and sizes to suit 
the various materials they are to handle, or the kind of heat-treatment. 

An instance of this is shown by the upright furnace in Fig. 89, which 
is for heating long bars or steel pieces. The heat is evenly distributed 
in the heating chamber by regulating burners F, which enter the furnace 
from four sides and on a tangent, so as to give the flames a swirling motion. 
They are controlled by the gas and air valves, A and G. For short lengths 
the upper burners E are shut off, and the section Y can be removed and 



Fig. 88. — Gas furnace with revolving retort. 

cover Z lowered. The large opening at / will give the necessary draft, 
and vents H can be used for peep-holes, while vent P allows the used 
gases to escape. 

Special designs of furnaces have been made for all of the various oper- 
ations of heat-treating, such as annealing, tempering, hardening, coloring, 
etc. Some of these have been made continuous operating and automatic 
as shown in Figs. 90 to 93 inclusive. In Figs. 90 and 91 is shown the fur- 
nace combined with a quenching bath, into which the work drops directly 
from the furnace. This quenching tank contains an automatic conveyer 
that lifts the work out of the tank and dumps it into a wheelbarrow shown 



166 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



in Fig. 91. Fig. 91 shows the details of the furnace as suppUed with a 
smooth Hning, and Fig. 92 shows the helical or worm lining that can be 
used with the same furnace if desired. The furnace is mounted in such 
a manner that its axis may be tilted at an angle, giving the revolving 
hearth an incline, with the discharge end lower than the entrance or feed 
end. The gradual inchne causes the material to feed forward, and by- 
means of a hand- wheel the degree of pitch may be adjusted so as to regu- 




FiG. 89. — Upright gas furnace. 



late the progression of the material through the furnace, and consequently 
the time of heating. 

The advantages of this method of automatic continuous heating are 
many: The material is charged in a hopper in bulk at one end of the fur- 
nace and fed automatically into the chamber. It comes continually 
in contact with the newly heated interior surface, which is revolving, 
thereby absorbing the heat from the lining as well as from the heated 
gases. In a stationary furnace the heat from the sides and roof are not 
utilized, as the material remains in a fixed position; that farthest removed 
from the heat requires a much longer period to be brought to the desired 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



167 



temperature and the more exposed pieces are liable to overheating, while 
others are insufficiently heated. To prevent oxidation, the end of the 




Fig. 90. — Automatic and continuous hardening furnace, with tilting mechanism. 

discharge spout may be carried beneath the level of the bath, thereby 
sealing it and excluding the air. 

In operation, the pieces are fed continuously into one end of the cylin- 




FlG. 91. — Details of continous hardening furnace, showing smooth interior. 

der. The furnace is fired internally from the opposite end, with the zone 
•of highest temperature at the discharge end. The cylinder revolves 
slowly (1 to 4 revolutions per minute), and owing to the slight inclina- 



168 



COMPOSITION AND HEAT-TREATMENT OF STEEI, 



tion of the furnace, the pieces treated fall slightly forward at each revo- 
lution, gradually progressing toward the discharge end, where they enter 
a proper receptacle or bath upon reaching the desired temperature. 

In certain classes of work, such as balls, nuts, and uniform shapes, 
the hehcal or worm type, as shown in Figs. 92 and 93, is used, but for 
irregular shapes, where the smooth lining can be used, the cost is less 
and a greater life is insured. Fig. 93 shows the details of construction 




Fig. 92. — Section of same furnace with 
helical or worm interior. 

of a furnace built on the same principle, with the exception that the work 
is held in a revolving retort, and the heating gases surround this in such 
a way that they do not come in contact with the work. 

Oil or gas fuel may be used and perfectly uniform results obtained, 
as the work treated is heated gradually with every portion of its surface 
exposed to the direct action of the hot gases and lining, and both tem- 




FiG. 93. — Sectional view of furnace with 
mufHed retort for work. 



perature and time are maintained constant. The furnaces are built 
to suit a wide range of requirements, and in sizes that will handle up to 
2000 pounds of stock per hour. While they were designed principally 
for hardening steel pieces, thej^ are also useful for annealing non-ferrous 
metals, such as brass cartridge shells, etc. 

Automatic apparatus has also been added to furnaces to carry the 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 169 

work through quenching and cleansing baths of various kinds. In one 
case an automatic gas-heating furnace discharges its work into a tank 
for quenching. The quenching tank contains a conveyer for removing 
it from the tank into receptacles with which it can be carried away. 
Two tanks can also be coupled together; into the first one of which the 
work is dumped from the furnace for quenching. From there it is con- 
veyed to the second tanl<:, in which the work is cleaned, and from there 
conveyed to pans, trays, or other articles with which it can be easily 
handled. The work drops from the furnace into the quenching bath 
in a continuous stream, and from the hopper it is fed through a perforated 




Fig. 94. — Gas booster to supply 
furnaces. 

barrel, that inclines down to the other end of the tank, where it is picked 
up by the conveyer and discharged from the tank. The perforated barrel 
revolves slowly to agitate the articles, thus bringing them in contact 
with the quenching liquid on all sides. The barrel end next to the hopper 
is movable, so it can be raised or lowered to make the work travel fast 
or slow. The liquid is admitted to the tank beneath the receiving end 
of the barrel, and as it becomes heated, by contact with the articles, it 
rises and is drained off, from the top of the tank, near the discharge end 
of the barrel. At the lower end of the barrel the pieces are picked up 
by the lower loops of an endless chain that is formed of buckets open on 
the inner side. They are elevated by this and dumped into a fixed hop- 
per within the upper loop of the chain, and from there the discharge chute 



170 COMPOSITION AND HEAT-TREATMENT OF STEEL 

leads them away from the tank. The buckets are perforated so as to 
strain the hquid from the pieces hardened. 

The double tanks may be used to quench work in the one, and then 
send it through a cleaning compound in the other. For instance, work 
that is quenched in oil may be sent through a second tank containing 
some liquid that will cut the oil from the work and leave it clean, or a 
liquid containing chemicals that act as a rust preventative may be used 
in the second tank. In fact there are many combinations for the double 
tank. 

The gas pipes from the street or the main in the street are sometimes 
found to be too small to supply the necessary gas to the furnaces when 
installing them. In this case a gas booster, similar to that shov/n in Fig. 
94, is used. This sucks the gas from the main faster than it would natu- 
rally flow, and delivers it to the furnaces as required. 

With gaseous fuels, it is probably as easy to control the temperature 
of furnaces to within a few degrees of a given point as with any fuel 
used. The latest invention along this line is the automatic apparatus, 
for controlling the temperature of gas furnaces. It was put on the market 
by the American Gas Furnace Company in December, 1909, and controls 
the temperature to within 5 degrees of a given point. Pyrometers being 
required to measure these high heats, the pointer on the pyrometer indi- 
cator was used as a starting point. The pointer was left free to oscillate 
back and forth as the temperature rises or falls in the furnace, as any- 
thing that would retard the action of this pointer would throw the 
pyrometer out of true and ruin it for accurate temperature readings. At 
the same time it was necessary to have power enough to instantaneously 
open and close the gas and air valves that admit the fuel to the furnace. 
The mechanism also had to be positive in its action. 

In Fig. 95 is shown a muffle gas furnace with the complete automatic 
temperature controlling apparatus attached thereto; Fig. 96 shows, on 
a much larger scale, the apparatus connected to the indicator; Figs. 97 
and 98 show the operating mechanism of the apparatus connected to 
the indicator, and Fig. 99 shows the apparatus connected to the furnace. 
The instrument operates as follows: 

In Fig. 95 the thermo-couple or hot end of the pyrometer is inserted 
into the furnace at A, and connected to the indicator at B. Underneath 
B is the mechanism shown in Fig. 96, while at C is that shown in Fig. 99. 
At D, in Fig. 96, is located a thumb screw that revolves the disk E and 
moves the pointer F with its arms, G, to the temperature at which it is 
desired to maintain the furnace. The arms G, as well as the rest of the 
mechanism, are operated by power supplied from a fan located in the 
case J. This is revolved by a current of air that is sent through a J-inch 
pipe, and blows against the blades of the fan. ■ 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



171 



How the arms G operate is best shown by the drawing, Fig. 97, which 
is a view that looks down on their top. When the temperature rises in 
the furnace, the indicator pointer / travels to the right until it passes 
under the left-hand arm G, which is now stationary, and comes in contact 
with the right-hand arm G, which is constantly oscillating in and out of 




Fig. 95. — Instrument for automatically controlling temperature of furnaces. 

slot H. When it arrives at the position shown, right-hand arm G grips 
it for an instant, and this trips the arm and throws it back to the posi- 
tion shown by left-hand arm G, so that the' indicator pointer I will pass 
it and register any rise in temperature which may occur after this, due 
to the lag. When right-hand arm G is thrown back to the stationary 



172 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



position, left-hand arm G is started oscillating in and out of slot H, by 
means of a cam. The valves that admit the gas and air into the furnace 
for fuel are then shut off, thereby stopping the heat. Then as the fur- 
nace cools and the indicator pointer / travels back to the left to record 
the lowering temperature, left-hand arm G catches it, trips, turns on the 
gas and air, and the right-hand arm G starts operating. 




Fig. 96. — Apparatus connected to the indicator. 



The arms G are given their oscillating motion or held stationary by 
the lower end riding on two disks K, that alternately act as cams and are 
fastened together, as shown in Figs. 96 and 98. The disks K are moved 
back and forth on their centers by piece L, which is moved back and forth 
the distance of the opening M. Piece L rides on bar N for one-half of 
this distance, and for the other half, the half round in the top in the open- 
ing M drops over the bar N and moves it back and forth to oscillate the 
disks K. While doing so, the end of bar N rides on a fiat spot in the valve 
rod 0, but when one of the arms G is tripped and the other starts oper- 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



173 



ating, the end of bar N pushes in or out the valve end 0, and opens or 
closes an air valve that sends a current of air into a diaphragm, or cuts 
it off, that is located in the lower part of the apparatus shown in Fif. 99. 
As will be seen in Fig. 98, one of the G arms is riding on the cam of the 
disk K, and is therefore in motion while the other G arm is riding on the 
outer circle and is therefore stationary. 

In the lower part of the apparatus two square holes are provided in 
the cylinder P, Fig. 95, to act as openings for the air and gas to pass through, 
and over these is a plate that raises and lowers to open and close them. 
The amount that these can be opened and closed is regulated by moving 
the arms R and S, in Fig. 99. These move the center rings up or down 
on the screw, and they can be clamped to it by the set screws back of the 



h'^n- 



Es. 97 




Fig. 98 



VV| 


iv 
K 


^ 


; 




■ 


L 


N 
—L 




Figs. 97 and 98. — Operating mechanism connected to indicator. 



arms, when the proper amount of motion for the valve slide is decided 
upon. The pin T is connected to the slide and allows it to be moved 
from the top to the bottom ring l)y the air that is admitted to or shut 
off from the diaphragm through the pipe U. 

One point on the arbitrary scale on the disk S means a motion of b\ 
of an inch for the valve slide, and when the arm R is placed at the "open" 
mark, and the arm S at the "shut" mark, the air and gas passages can 
be opened or closed by the slides traveling their full distance. This is 
seldom done, however, as the furnace can usually be regulated by turning 
on or shutting off a part of the heat. 

This apparatus promises to fill a long-felt want in furnaces for heat- 
treating metals, as any one who operates them knows how difficult it is 
to keep the temperature at a certain given point by hand-operated valves. 



174 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



HEATING IN LIQUIDS 



Furnaces using liquid for heating consist of a receptable to hold the 
liquid, and a chamber underneath and around its sides that is heated 
by coal, oil, gas, or electricity; the liquid being kept at the highest tem- 




FiG. 99. — Apparatus connected to the furnace. 



perature to which the piece should be heated. The piece should be heated 
slowly in an ordinary furnace to about 800° F., after which it should be 
immersed in the liquid bath and kept there long enough to attain the 
temperature of the bath and then removed to be annealed or hardened. 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 175 

The bath usually consists of lead, although antimony, cyanide of 
potassium, chloride of barium, a mixture of chloride of barium and chloride 
of potassium in different proportion, mercury, common salt, and metallic 
salts have been used successfully. 

This method gives good results, as no portion of the piece to be treated 
can reach a temperature above that of the liquid bath; a pyrometer attach- 
ment will indicate exactly when the piece has arrived at that temperature, 




Fig. 100. — Oil or gas lead (or oil) batli furnace. 



and its surface cannot be acted upon chemically. The bath can be main- 
tained easily at the proper temperature, and the entire process is under 
perfect control. 

When lead is used it is liable to stick to the steel and retard the cool- 
ing of the spots where it adheres. This can be overcome to a large extent 
by using a wire brush to clean the work with. A better method, however, 
is to heat the piece to a blue color, which is about 600° F., then dip it 



176 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



quickly in a strong salt water, and then heat it in the lead bath to the 
hardening temperature. By dipping in and out of the brine quickly 
the piece is completely coated with salt and this prevents the lead from 
sticking to the piece when heating it for hardening. 

The greatest objection to the lead bath is that impurities such as 
sulphur, etc., are liable to be absorbed by the steel, and thus alter its 
chemical composition. This is especially so if the lead bath is used for 
the hardening heats, as at these high temperatures steel has a great affinity 
for certain impurities. A notable example of this is its greatly increased 
attraction for oxygen, which the metal absorbs aiid retains as oxides 




Fig. 101. — Lead bath furnace with hood. 

and occluded gases. With high temperatures lead and cyanide of potas- 
sium throw off poisonous vapors which make them prohibitive, and even 
at comparatively low temperatures these vapors are detrimental to the 
health of the workmen in the hardening room. I'he metallic salts, how- 
ever, do not give off these posionous vapors, hence are much better to 
use for this purpose; but many times the fumes are unbearable. 

When the lead bath is only used for the lower tempering heats the 
furnace shown in Fig. 100 is a good design. It can use either gas or oil 
for fuel, and is supplied with a high-temperature thermometer to measure 
the heat of the bath. This should never be higher than is desired for 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 177 

drawing the temper. It is a great improvement, even with this furnace, 
to place a hood over it that is piped to the outside of the building, and 
has a good draft, to carry away any fumes that may arise from the bath. 
This is an absolute necessity, however, when the lead bath is used for the 
hardening heats, and for that reason a furnace, with its own hood, similar 
to that shown in Fig. 101, is much better. These of course can be obtained 
or made with any size or shape of lead pot that is required for the work 
to be heat-treated. 

Cyanide of potassium when applied to steel that has been heated to 




Fig. 102. — Gas furnace for pot of 
cyanide. 

a red heat reduces the oxides and causes any scale that may have formed 
on the metal to peel off. Thus soft spots that may be caused by scale 
or blisters when hardening steel can be abolished by dusting cyanide 
on the piece before quenching it. It, however, has another use in heat- 
treating steel, as when the metal is heated to a red heat, in a cyanide 
bath, it slightly carbonizes the surface and is thus used quite extensively 
for case-hardening. It should be kept at the boiling point and the metal 
submerged in it for about 5 minutes and then quenched. This has resulted 
in the building of a special furnace for heating cyanide, as shown in Fig. 



178 COMPOSITION AND HEAT-TREATMENT OF STEEL 

102. Here the cyanide pot P is suspended by its flange over a chamber 
filled with the gas flames, and hood H gathers the flames and carries them 
out through pipe S. 

Molten cyanide sputters and drops fly, like red-hot bullets, and conse- 
quently many bad burns are caused by its use. The fumes arising from 
the pot are also very poisonous, and the cyanide of potassium itself is a 
rank poison. It is therefore a dangerous product to use. Tools dipped 
in powdered cyanide and quenched in a bath causes the bath to become 
very poisonous, and the hand should never be put in the bath to take 
pieces out, as running sores that are hard to heal may be the result. Cya- 
nide is also injurious to high-carbon or high-speed steels, and as there are 
many other chemicals coming into use that will do everything that cya- 
nide will do, and some things that it will not do, this material is fast going 
out of use as a factor in heat-treating steel. The metallic salts are taking 
its place and doing much better work, and they are not poisonous. 

A barium-chloride bath offers all the advantages obtained from a lead 
bath, or cj^anide, and to this is added the advantage of the barium chloride 
forming a coating on the steel, while it is being transferred from the heat- 
ing bath to the quenching bath. This prevents the metal from becoming 
oxidized, by keeping it from coming in contact with the oxygen in the 
air. It also volatilizes at a much higher temperature than lead, or any 
of the other materials used for heating baths, and therefore is success- 
fully used for the high temperatures that are needed to harden high- 
speed steels. 

As pieces heated in this bath have the temperature raised evenly, 
and at the same time, on all sides or exposed parts, it overcomes, to a 
very great extent, the tendency of warping or distortion which all steels 
have. 

While barium chloride forms a coating on the steel heated in it, this 
coating usually peels off when suddenly cooled in the quenching bath, 
and any which might cling to the metal is easily brushed off, or it can 
be jarred off by hitting the tool a sharp rap. This is also considerable 
of an advantage over the lead, or other baths, used for heating steel, 
as frequently spots of lead adhere to the steel and are difficult to remove. 

In Fig. 103 is shown a gas or oil burning furnace that was designed 
especially for barium chloride. It is composed of a sheet-metal shell 
that is lined with a special fire-brick to withstand the high temperatures 
that are required. A graphite crucible is used to hold the chloride. 
After the crucible is set in the furnace, the top, which fits close to the 
crucible, is placed on. This top is made of the same special fire-brick 
that forms the lining of the furnace, and it is held together by a sheet- 
metal band with two lugs and a clamping nut. This band is provided 
with two handles to make it easily movable when the crucible burns out 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



179 



and it is necessary to take this out and insert a new one. The opening 
between the furnace top and the crucible should be sealed with fire-clay 
to prevent the gas flames from attacking the barium chloride in the cru- 
cible, as this causes unnecessary fumes, that are almost unbearable, to 
come from the bath. Two per cent, of soda ash (carbonate of soda) is 
sometimes added to prevent these fumes. 

The gas is sent into the furnace at an angle, as this gives the flame 
a rotary motion that will create an even heat on all sides of the crucible. 




Fig. 103. — Gas or oil heated barium chloride furnace. 



The exhaust opening is placed at the side of the gas inlet, and as close 
to it as possible, so the gas will make the complete circuit of the furnace 
chamber. 

In Fig. 104 is showTi a line drawing of the same furnace, supplied with 
an enclosed hood permanently fitted to it; entrance being obtained by 
means of a large door. Through this hood the fumes of the chloride 
are carried away and the burned gases are taken from the furnace through 
a pipe up into the top of the hood and thence out the chimney. 



180 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



In heating steels for hardening that do not require a temperature 
of over 1650° F., a mixture of chloride of barium and chloride of potas- 
sium, in equal parts, gives the best results. As the required temperature 
increases the chloride of potassium should be reduced, until when 2000° 
F. is reached it should be left out altogether and only the pure chloride 
of barium used. In all cases the steel should be heated slowly to from 
600° to 800° F. before it is immersed in the chloride bath, and if slowly 
heated to a higher temperature it will do no harm. 

With the furnaces shown above, steel cannot be heated to over 
2100° F. without its becoming pitted, and with many high-speed steels 
it is desirous to heat them to nearly 2500°. This is doubtless due to the 




Fig. 104. — Barium chloride furnace with hood. 



fact that a graphite crucible is used and particles of it separate from 
the crucible and float in the chloride bath until the metal is inserted, 
when they attack it and cause pits to form. With an electric furnace, 
such as is shown in Fig. 108, this is entirely overcome, as the chloride 
holder can be made of fire-brick and electrodes inserted in the bath. 
Owing to the heats being generated inside of the bath, instead of sur- 
rounding the pot, a thin-walled crucible is not required, hence the 
chloride pot can be built up of fire-brick of any thickness that will give 
it the needed strength. 

In starting up for the first time the crucible should be filled with the 
barium-chloride that can be bought in 1000-pound casks, at about 3 cents 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 



181 



per pound, and this heated slowly until it melts down. After this more 
mixture should be added until the crucible is nearly full. After the bath 
is melted, tests should be made with a pyrometer until it is found hot 
enough for hardening. When through for the day the bath should be 
allowed to cool with the furnace, and when started again it should 
be heated up slowly. 

After the bath is thoroughly liquid, take a piece of steel with a ground 
or machined surface, heat it to the temperature of the barium and dip 
it in the cooling bath, then brush it off. and if there are no "bubbles" 




Fig. 105. — Experimental electi-ic furnace for heat-treating steel. 



or "blisters" on the piece, heat the bath to a higher temperature and 
repeat the operation until they do appear, and then note the temperature 
shown by the pyromieter. For reg;ular use a temperatiu-e about 50° 
below the point at which bubbles appear is the best; the test being made 
with a new clean bath. These bubbles are the indicators of the pitting 
that occurs at temperatures of 2100° F. or over when the gas or oil fur- 
nace is used for heating the barium chloride. As the bath becomes old 
or dirty, and sluggish from steel scale, etc., bubbles will sometimes appear 
at a lower temperature than they should, in which case the remedy is a 
fresh bath in the crucible. 



182 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



ELECTRIC FURNACES 



While the cost of electricity as a fuel for heating furnaces is probably 
greater than that of any of the others, the results obtained by its use 
in heat-treating steel are better than that of any known method. 




Fig. 106. — Magnetic furnace for hardening steel. 



The electric furnaces might be placed in two classes; namely, those 
which use electrodes and those which have the receptacle wound with 
platinum, nickel, or ferro-nickel wire, which is covered with some product 
that will protect it from silication due to the silicates of the receptacle; 
calcium aluminate being one of these. Both of these furnaces are lined 
with some refractory material, but the latter is not practical for large 



FURNACES AND FUELS USED FOR HEAT-TREATMENT 183 

furnaces, hence is used for very small work or for experimental purposes. 
This style of furnace is shown in Fig. 105. 

In Figs. 106 and 107 is shown an electric furnace in which the elec- 
trodes are used as a magnet to hold the work until it reaches the point 
of recalescence, which is non-magnetic. The magnetic attraction is then 
broken and the work can drop into a bath for quenching. This will 
give it the greatest hardness it is possible to give the steel, and at the 
same time make the grain as fine and the molecules as cohesive as they 
can be made by heat treatment. 

Electric furnaces similar to that shown in Fig. 108 are used to heat 
the liquid baths described above. In this furnace the metaUic salt baths 




PHO 

Fig. 107. — Section through muffle of 
magnetic furnace. 



seem to be the hiost appropriate. These salts conipletely prevent con- 
tact between the white hot steel and the air during the heating, as well 
as during the passage to the quenching bath; the steel being uniformly 
covered with a protective coat of the salts during the passage of the steel 
from the furnace to the quenching bath. On immersion in the cooling 
liquid this coating immediately leaves it and the surface of the steel always 
appears smooth. The formation of scale is entirely prevented even after 
tempering. 

The source of heat being inside the bath in this furnace the heat is 
evenly distributed and the temperature of the bath is uniform throughout 
every part of it. High temperatures are as readily obtained, and with 
as little watchfulness, as relatively low ones, which makes it easy to 
determine the temperatures desired in heat-treating the steel. 



184 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



The pyrometer can be used successfully in measuring the temperature 
of the bath. The current traversing the bath varies, and the temperature 
and the primary current remain constant. One careful determination 
with the pyrometer is enough to afterward judge the temperature of 
the bath entirely by the current. 





Fig. 108. — Sectional views of electrode furnace. 



This style of furnace requires from 15 to 40 minutes to start, accord- 
ing to the size. The cold furnace can be started by passing the current 
through a piece of carbon until this becomes white hot and melts the 
surrounding salt, which then becomes conductive and in turn melts the 
whole mass. When finished using the current is shut off and the salt 
bath can be kept molten for a long time by putting a cover over it. 



CHAPTER IX 

Annealing Steel 

theory, methods, materials used and appijcation 

If the best results are desired from steel, after it has been rolled, forged, 
pressed, cast, or put into workable shapes in any other way, it should 
be annealed before any other work is done upon. it. This removes the 
internal strains that are set up in the metal, when working it into the 
desired shape for future operation, and also softens the steel. It can 
then be more economically machined with any kind of cutting tools, 
can be heat-treated in various ways without the danger of cracks forming, 
and will have greater qualities of strength and endurance when put to 
its intended use. 

The annealing of steel consists of the thermal treatment used in carry- 
ing it above the temperature at which its highest ptoint of transformation 
occurs, and then allowing it to cool gradually. This point of transforma- 
tion is that at which the steel becomes non-magnetic and its physical 
structure changes. If a pyrometer is used to measure the temperature 
of the steel in heating or cooling, it will show a point at which the rapid 
change in temperature ceases for a time, and the recording chart will 
show a line nearly at right angles to that of the rise or fall curve. At 
this point the change in structure of the metal ceases until all the mole- 
cules have become thoroughly non-magnetic and a new crystal-size of 
grain is born. This refines any large or coarse crystals that may have 
been produced in the steel by former methods of heating or working. 
This change in structure releases any strains which may have been set 
up in the metal, and allows them to readjust themselves so that they 
are equalized throughout all parts of the piece. 

This temperature of the point of transformation varies considerably 
in different steels. This is partly shown by Fig. 109, which was plotted 
from two recording pyrometer charts. Steels vary more widely than 
this, however, in their highest recalescent point; it being affected by the 
various ingredients that are alloyed with the metal. 

Another operation is sometimes called annealing, that is, that of par- 
tially destroying the effects of sudden cooling or quenching. In this 
the annealing temperature is kept below the highest point of transforma- 

185 



186 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



tion. This operation is more properly named tempering, and will be 
dealt with under that title. 

As a general rule all steel should be annealed after every process 
in manufacturing that tends to throw it out of its equilibrium, such as 
forging, rolling, and rough machining, so as to return it to its natural 
state of repose. It should also be annealed before quenching, case- 
hardening, or carbonizing. 

When a steel ingot has been poured and subjected to the hammering 
process, that is nearly always its first mechanical working operation, 
there is a tendency for the crystals to crush, that form the mass of the 
metal whether it be hammered hot or cold. This will bring the par- 



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Fig. 109. — Recalescent point curves, plotted from two pyrometer charts. 

tides of the metal closer together, but there is a hmit to the increase in 
the density which can be attained in this manner as a great deformation 
is eventually given the metal. This metal is called "hammer-hard," 
and a large number of metals will show about twice the tensile strength 
after being hammered to the limit of compression that they will when in 
the normal state. 

The limit of compression is difficult to gage, and if passed, as it usually 
is in practice, the hammering is liable to cause coarser crystals to form 
where it has squeezed out from under the hammer blows. To remove 
this crystallization and refine the grain, annealing has to be resorted to. 
Thus certain laws have been formulated which hold good on annealing 
hammered metal, and these are as follows: 



ANNEALING STEEL 187 

First. — Annealing cannot be done instantaneously, but its effects 
are the greater in proportion to the time consumed. A rapid change takes 
place at the start, but this is slower and slower as the time progresses, 
and there is a tendency toward a fixed limit for the decrease in hammer- 
hardness at each degree of temperature. 

Second. — The higher the annealing temperature, the lower will be 
the limit toward which hammer-hardness tends; in practice the more 
rapidly will this limit be attained. 

Third. — The annealing effects are practically completed when a 
certain temperature has been reached, and any increase above that does 
not further reduce the tensile strength as this has reacVied the lowest 
point possible for the steel operated on. 

The effect called " crystaUization of annealing" may start at this tem- 
perature and become more pronounced as the annealing process con- 
tinues. It causes the reduction of area to decrease, and if very pronounced 
this may become nil, together with the elongation and tensile strength. 
Another phenomenon might be mentioned here, and that is spontaneous 
annealing. Thus if hardened steel be left to itself it will aimeal of itself, 
the only factor entering into this phenomenon being time. As this time, 
however, covers such a long period and the annealing process is such a 
slow one the principle is of no importance from a practical standpoint. 

From the above may be deduced three practical rules to adopt in anneal- 
ing steel, these being: 

First. — A quenched or hammered piece must be heated to a tem- 
perature above its highest point of transformation, but as close to this 
point as possible. 

Second. — This temperature must be retained long enough to allow 
the entire piece to reach an even temperature, but it must not be 
prolonged beyond it. 

Third. — The rate of cooling must be sufficiently slow to prevent 
any hardening taking place, not even superficial hardening. 

In applying these rules we find that extra low-carbon steel should 
be annealed at 1650° F., and extra high-carbon steel at 1375°. The 
time of annealing varies with the size and shape of the piece as well as 
with the work which it has to perform. The more important this work 
is, the more prolonged should be the annealing process. Intricate pieces 
with thin and thick sections have to be handled with extra care, and some- 
times materials are brought into use to retard the cooling of the thin 
section faster than the thick one, as ordinarily a thin section v/ill cool 
quickly in comparison with the thick one, and consequently be that much 
harder. 

To insure slow cooling, when a slow-cooling furnace is not obtainable, 
the work should be packed in some non-carbonizing material, in an iron 



188 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



box lined with fire-brick siniilar to the one shown in Fig. 110. The whole 
can then be heated in a furnace and set out on the floor to cool as the 
thickness of the materials prevents rapid cooling. This will also tend 
to prevent the pieces from scaling as they do not come in contact with 
the oxidizing influences of the atmosphere. When the temperature of 
the pieces has dropped to 550° F. they may be removed from the box 
as the annealing process has ceased, and there will be no danger of their 
air-hardening. 

As it is generally agreed upon that steel should not be heated much 
above the point of transformation in the annealing process it would be 
well to give the reasons. The nine laws formulated by Prof. H. M. Howe, 
after many tests by himself and others, cover the ground so thoroughly 
that they are here given. 

First Law. — When a given steel is heated to a temperature above 
the highest point of transformation the grain assumes a definite size, 
characteristic of the temperature. We call this the normal size. 




Fig. 110. — Cast-iron box for annealing. 



Second Law. — The size of the grain increases in proportion to the 
temperature, counted from the highest point of transformation. 

Third Laio. — The influence of the temperature is the more pronounced 
the greater the carbon component of the steel. In other words, for the 
same annealing temperature the normal grain of the steel is coarser the 
greater the carbon component. 

Fourth Law. — If a steel is raised to a temperature above its highest 
point of transformation, and if in consequence of previous treatment 
the steel possesses a finer grain than the normal, the grain of the metal 
becomes coarser until it is equal to the normal grain. 

Fifth Law. — In order to attain the normal grain for any temperature, 
the metal must be maintained at this temperature for some time. 

Sixth Law. — If the metal is heated to a certain temperattire and has 
assumed the normal grain for this temperature, and if it is then main- 
tained at a somewhat lower temperature, but still above the point of 



ANNEALING STEEL 189 

transformation, the size of the grain is not reduced, provided the metal 
is not reduced below the point of transformation. 

To illustrate this, if a steel is carried to 2200° F. ; the grain then becomes 
of the size characteristic of this temperature; if the temperature is then 
lowered to 1650° there will be no change in the size of the grain. It would 
be quite different, however, if instead of cooling the metal directly to 
1650°, it had been cooled do^vTl to 925°, which is much below the point 
of transformation, and then reheated to 1650°. 

Seventh Law. — If the temperature of a steel remains below the point 
of transform.ation its grain does not change. 

Eighth Law. — If a steel is cooled slowly after having been heated to 
above its point of transformation, it possesses substantially the same 
grain as that which it possessed at the maximum temperature. 

Ninth Law. — From this it may be deduced that the grain of a metal, 
after annealing, is the coarser the higher the temperature to which it 
has been raised above the point of transformation. 

While the relation existing between the annealing temperature and 
the mechanical properties has not been fully determined, enough is known 
to establish certain rules that are beneficial in a practical way. A 
coarse-grained metal is more brittle than a fine-grained, and therefore 
any change in the size of the grain will affect the strength of the steel. 
As the annealing temperature affects the size of the grain, a steel that 
is heated to a variable temperature and slowly cooled will alter its mechan- 
ical properties about as follows: 

First. — The tensile strength slightly increases with the increase in 
temperature up to 2375° F., after which it rapidly decreases. This makes 
it necessary to keep the annealing temperature a little above, but as close 
to the point of transformation as possible. 

Second. — The elastic limit passes through a minimum at the highest 
point of transformation, but increases slightly when the temperature 
passes this point, and then decreases as this point is exceeded by 175° F. 
The slower it is cooled from the point to which it has been heated the 
lower will be the elastic limit. 

Third. — The elongation decreases as the annealing temperature 
increases, and this decrease is very important when the temperature 
attains 2375° F. 

With these points taken into consideration it will be seen that the 
annealing of steels cannot be too carefully done if the best results are 
to be obtained, and especially is this so of the high-grade alloy steels 
which are being used more and more every day. It has been shown 
that if the heat treatment is carried out in a manner that will produce 
sorbite, the tensile strength is nmch higher and the elongation is slightly 
greater than when the metal is simply annealed. To obtain sorbite it 



190 COMPOSITION AND HEAT-TREATMENT OF STEEL 

is necessary to quench above the point of transformation and then reheat 
to from 575° to 1300° F., according to the composition of the metal and 
the hardness desired^ then cool in air or in water. 

APPARATUS FOR ANNEALING 

The furnaces used for annealing are the same as those used for other 
heat-treating operations, unless enough pieces are annealed to install a 
slow-cooling furnace, and then it is only the accessories that are different. 
The materials in which to pack the metal are nearly as numerous as the 
baths for quenching, and where a few years ago the ashes from the forge 
were all that were considered necessary for properly annealing a piece 
of steel, to-day many special preparations are being manufactured and 
sold for this purpose. 

The more common materials used for annealing are powdered char- 
coal, charred bone, charred leather, mica, slacked lime, sawdust, sand, 
fire-clay, magnesia, or refractory earth. The piece to be annealed is usually 
packed in a cast-iron box, similar to Fig. 110; using some of these materials 
or combinations of them for the packing, the whole is then heated in a 
furnace to the proper temperature and set aside, with the cover left on, 
to cool gradually to the atmospheric temperature. 

For certain grades of steel these materials give good results; but for 
all kinds of steels and for all grades of annealing, the slow-cooling furnace 
no doubt gives the best satisfaction, as the temperature can be easily 
raised to the right point, kept there as long as necessary, and then regu- 
lated to cool down automatically and as slowly as is desired. The gas, 
oil, or electric furnaces are the easiest to handle and regulate. 

As an example of this a maker of high-grade files uses a gas furnace 
in which to anneal the files, and they are packed in this with the tangs 
outward. The furnace is heated up and kept at a temperature of 1500° F. 
for 4 hours, and then allowed to slowly cool during two nights and one 
day. The flame is from a vaporized naphtha preparation that is free from 
injurious elements, such as sulphur, as is supplied with a slight under- 
supply of oxygen, so there will be no danger of its combining with the metal 
and oxidizing it. The files are submitted to the direct action of this 
flame, which fills every part of the heating chamber, so that the end and 
sides, as well as the center, can be maintained at the same even tem- 
perature. By having a constant pressure and volume for the air and 
gas the flame is easily controlled and is non-oxidizing, therefore there is 
no pitting or blistering of the files. They do, however, have a very 
thin scale, that is caused by the air that leaks into the furnace while it 
is cooling, but this is not enough to do am' practical damage. 

There is one notable exception to these annealing rules, and that is 
in the case of Hatfield's manganese steel, which is so brittle when cast 



ANNEALING STEEL 191 

as to be useless. It is toughened, or tempered, by heating and quench- 
ing, and is hardened by slow cooling. 

While high-speed steel has heretofore been annealed in practically 
the same way as the carbon steels, and therefore subject to the above 
rules, it is hardened by rules altogether different from those governing 
the carbon steels. 

A new method of annealing high-speed steel that is a great improve- 
ment over this old one has been discovered and perfected by C. U. Scott 
of Davenport, Iowa, at the Rock Island arsenal. He places the high- 
speed steel in a furnace that is heated to not over 750 °F., and raises the 
temperature slowly to 1300° F. He then shuts off the heat and allows 
both the steel and the furnace to cool to not over 750° F., or to atmos- 
pheric temperature if desired. The steel is then reheated to a temper- 
ature of 1300° F., and held there for 30 minutes and then cooled in the 
air. 

In this way any high-speed steel that is not over 1 inch square can 
be annealed in 40 minutes, and it does not take over one hour for large 
stock. The metal is made as soft and it machines as readily as steel 
annealed by any other method. Whether the steel is entirely cooled 
after the first heating or whether the temperature varies a few degrees 
from the 1300 is immaterial. 

Another hardener on trying out this method got his data mixed and 
obtained the same degree of softness in another way. He heated the 
steel to a low red, and held the temperature at that point for 30 minutes. 
He then let it cool down and afterward reheated it and immediately 
let it cool down until it was at the correct temperature for water anneahng 
and then laid it in the ashes until it was cold enough to handle. 



CHAPTER X 

Hardening Steel 

alterations in structure, influence of composition, and results 

obtained 

Hardening, when applied to steel, is generally understood to mean 
the heating of the metal to a high temperature and then plunging it into 
a bath for the purpose of suddenly cooling it. "While this definition holds 
good on most steels, a few alloying materials now used reverse this and 
make the metals air-hardening, that is, their hardest and toughest state 
is obtained by a slow-cooling process rather than a sudden one. 

Two reasons might be assigned for the desirability of hardening steel, 
and these are: First, to give the steel a cutting edge such as is required 
for all cutting tools, and, second, to alter the static strength and dynamic 
qualities of the metal so it will give the best results for the moving parts 
of machinery. 

In this second case steels may be altered by quenching from a high 
temperature and tempering, to an extent that will greatly improve their 
wearing qualities, tensile strength, elastic limit, magnetic qualities, or 
resistance to shock, and yet not be capable of attaining a hardness that 
will not allow a file to cut it; this being the usual test of hardness api^lied 
in the shop. Thus, generally speaking, all steels may be hardened, 
although some may have a low carbon content. 

To harden steel, therefore, it is necessary for the heating to produce 
a change in the structure, and that the quenching, which follows the 
heating, retains a whole or a part of the elements produced by this 
change of structure. It is therefore necessary, as in annealing, that the 
temperature of the steel be raised to a point slightly above the point of 
transformation or upper recalescent i:ioint. 

As the point of transformation varies with different ingredients which 
are alloyed with steel, it is necessary to find out where this point is in 
the steel to be hardened. A steel may be heated to 1300° F. — which 
is above the point of transformation in some steels — and no change in 
structure will take place, and therefore no results in hardness will be 
obtained. If the same piece is heated to 1650° — which we will consider 
the point of transformation in this piece — the intermolecular transforma- 

192 



HARDENING STEEL 193 

tion, which consists of the passage of the carbon from the combined into 
the dissolved state, will take place and the steel will assume the hardest 
state it is capable of, if properly cooled. 

Thus the factors that have an influence on the results of hard(>ning 
are: First, the nature and composition of the metal; second, the tem- 
perature of the metal when quenched, and, third, the nature, volume, 
and tem.perature of the quenching bath, 

MICROSCOPICAL EXAMINATION 

The nature of these different factors is sIioaati to a large extent by 
quenching the metal at different temperatures, polishing the surface, 
attacking it with picric acid, tincture of iodine, hydrofiuoric acid, or 
any other etching materials and examining it under a microscope. 

Fekeitk. — Steel containing less than 0.85% carbon will show small 
dark masses, if etched with picric acid, which are the more numerous 
the closer the carbon content is to 0.85%. At this percentage they cover 
the entire surface. These masses show alternate layers which are fer- 
rite — pure iron — and an iron carbide called cementite. The ferrite 
being the softest constituent of steel, it will indent when polished and 
the cementite will stand out in relief. 

Ferrite is the carrier for all of the alloying elements in the high-grade 
steels. It is the principal constituent of all steels and the predominating 
one in low-carbon steels. It has one peculiarity which is very important, 
and that is, that when heated to about 1400° F. it undergoes a sudden 
change which is shown by its absorption of heat. It then loses nearly 
all of its power to attract a magnet as well as changing its specific heat 
and several other properties. No alteration, however, takes place in its 
chemical composition. 

At 1550° F. it again shows changes by absorbing heat and its prop- 
erties are again changed. (See chart 1, page 67.) Its electrical conduc- 
tivity has changed and it is far less brittle. These changes occur both 
in the rise and fall of the temperature, and have been called by different 
metallurgists the points of transformation, the recalescence points and 
the critical temperatures; all of which mean the same. 

Ferrite is shown in Figs. Ill, 112, 113, 114, and 117. 

Cementite is the carbide of iron, and is expressed by the following 
formula: FesC, which means ferrite — which is pure iron — 3 atoms 
for every one atom of carbon. It is the second constituent in importance 
in steel — ferrite being first — and is very hard and brittle. Practically 
all of the carbon is present in this form, and it usually crystaUizes in 
thin flat plates. Cementite does not exist in pure iron, which contains 
no carbon, and of itself contains about 6.6% of carbon, which is about 



194 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



one-fifteenth of it. Two extremes of cementite formation are shown 
in Figs. Ill and 112. 

Pearlite. — Pearlite is an intimate mixture of ferrite and cementite, 




Fig. 111. — Ferrite with very thin con- 
tinuous cementite skeleton. Low car- 
bon. Magnified 250 diameters. 



Fig. 112. — Ferrite, white. Cementite, 
black. Magnified 250 diameters. 



and consists in general of 32 parts ferrite to 5 of cementite, which gives it 
the appearance of mother of pearl, from which it derives its name. It 
exists in a lamellar formation, which is alternate plates of ferrite and 




Fig. 113. — Ferrite matrix with sepa- 
rated pearlite islands. Magnified 
250 diameters. 



Fig. 114. — Ferrite, white. Pearlite, 
black. Magnified 250 diameters. 



cementite, or in a granular formation, which is intermingling grains of 
ferrite and cementite. If commercial steels were free of graphite they 
would hold nearly fixed proportions of ferrite, cementite, and pearlite, all 



HARDENING STEEL 195 

combined, as these steels seldom exceed 1.40% carbon. A normal steel, 
containing 0.85% carbon, would then consists of 100% pearlite, while 
below this carbon content the whole carbon would be divided into 
pearlite and excess ferrite. If the total carbon exceeds 0.85% and is all 
combined, the excess would be cementite instead of ferrite, and the cemen- 
tite would increase with the carbon. Pearlite is shown in Figs. 113 and 114. 

Marten SITE and H a.rdenite. — Leaving the steels that have been 
cooled slowly, and taking up those which have been quenched from a 
given temperature, and hardened, we find that a steel containing about 
0.85% carbon, if heated to about 1400° F. and quenched, will show under 
the microscope extremely fine lines intersecting each other in the direc- 
tion of the sides of an equilateral triangle. This constituent has been 
named martensite in honor of Professor Martens. It is the principal 
constituent of all ordinary hardened steels that have a carbon content 
above 0.16%, and tempered steels owe their quality of hardness to it. 
It is so hard that a needle will not scratch it after the metal has been 
polished. 

In steels containing over 0.85% carbon the martensite is said to be 
saturated and shows slightly different under the microscope. This has 
been called hardenite by some, which word is often used in French and 
German books. 

Martensite is shown in Figs. 115 and 116. 

Sorbite is a constituent between cementite and pearlite, and chiefly 
differs from the pearlite and cementite by the crystals of these segre- 
gating and not quite perfectly developing. This is drawing the line pretty 
fine, but the sorbitic structure is finer than the pearlitic, and it is con- 
sidered the extreme opposite of the crystalline structure. The sorbitic 
structure is considered necessary in metals that have to resist wear and 
erosion, and the natural formation of this structure is rendered possible 
by the addition of certain alloying elements. In hardened steel, sorbite 
is considered as the transition from cementite to martensite. 

The sorbitic structure may be obtained when the cooling is not as 
rapid as that of quenching, but still much faster than the slow cooling 
for annealing; by quenching immediately below, or just at the end of 
cooling through the critical range; by cooling pretty fast through the 
critical range without actual quenching; or by rapidly cooling the steel 
and then reheating to about 1100° F. Sorbite is not clearly defined in 
micro-photographs, but Fig. 117 shows it fairly well, with ferrite. 

Atjstenite. — High-carbon steels that contain over 1.10% of carbon 
and are suddenly cooled from a temperature of 2000° F. will show a con- 
stituent, in addition to martensite, which may be distinguished from it 
by a different color. If etched with nitrate of ammonia, or with a 10% 
solution of hydrochloric acid, it will show white. This constituent is 



196 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



softer than martensite, and is easily scratched with a needle. It is essen- 
tially a conglomeration of ferrite and cementite. It has been named 
austenite after Prof. Robert Austen. 




Fig. 115. — Martensite formation. 
Magnified 250 diameters. 



F.G. 116.— Martensite. Magnified 200 
diameters. 



Austenite is difficult to preserve throughout the whole structure of 
the steel. Quenching in a bath that has a temperature below the freezing 
point, or any other means which will cool it rapidly, will aid in preserving 




Fig. 117. — Ferrite and sorbite. 
Magnified 250 diameters. 



Fig. 118. — Austenite, white. Troostite, 
black. Magnified 50 diameters. 



it. Tempering the metal afterward, however, loosens the austenite, and 
it is not of much practical use owing to the high temperature at which 
it is obtained. Fig. 118 shows the austenite formation. 



HARDENING STEEL 197 

Troostite. — If the steel is quenched during or just above its trans- 
formation in a bath of little activity, such as oil, or if it is hardened in 
the usual way and then tempered, we can obtain a constituent which 
will show jet black if polished and etched with picric acid, or if etched 
with a tincture of iodine it will show white. This has been named troostite 
in honor of Prof. M. Troost. 

Troostite is also softer than martensite, as it can be scratched with 
a needle. It holds some ferrite, austenite, or cementite, or a combination 
of these, and is found plentifully in tempered steels as it is a product of 
the usual tempering operations. It shades gradually into the sorbite, 
but is very sharp in its divisions from martensite. Troostite is sho\vn 
black in Fig. 118 and white in Fig. 119. 




Fig. 119. — Martensite, black. Troostite, 
white. Magnified 350 diameters. 

In subjecting steel to different heat treatments we can change the 
constituents from pearlite to martensite or hardenite, sorbite, austenite, 
and troostite, and back again through these different stages, and by exam- 
ining them with the microscope we can judge very closely the treatment 
they have been subjected to. 

By making these changes we also change its constitution, its static 
strengths, and its dynamic properties. This is where the practical appli- 
cation of this knowledge aids the engineer or designer in designing the 
moving as well as other parts of machinery so as to get the best results 
from the smallest quantity of material. 

EFFECT OP COMPOSITION AND HARDENING 

The constitution of a given steel is not the same in the hardened as 
in the normal state, owing to the carbon not being in the same state. 
In the annealed or normal steel it is in a free state, while in a hardened 



198 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



steel it is in a state of solution, which we may call martensite; and this 
contains more or less carbon according to the original carbon content 
of the steel. The composition, and therefore the mechanical properties, 
depend principally upon the carbon content, the mechanical properties 
being changed slowly and gradually by an increase in carbon. 





Table 1. Composition 










Carboniz- 
ing Steel 


Very Low 
Carbon 


Low 
Carbon 


Medium 
Carbon 


High 

Carbon 


Vefy High 
Carbon 


Carbon 


0.10 


0.14 


0.23 


0.52 


0.60 


0.72 


Silicon 


0.09 


0.05 


0.15 


0.18 


0.10 


6.17 


Manganese 


0.19 


0.33 


0.45 


0.35 


0.40 


0.38 


Phosphorus 


0.016 


0.023 


0.091 


0.021 


0.035 


0.03 


Sulphur 


0.025 


0.052 


0.062 


0.043 


0.025 


0.06 



MECHANICAL PROPERTIES WHEN ANNEALED 



Tensile Strength (in pounds 
per square inch) 

Elastic Limit (in pounds per 
square inch) 

Elongation (percentage in 2 
inches) 



60,300 


61,500 


66,500 


97,800 


116,400 


36,300 


35,200 


41,200 


52,600 


66,500 


29 


27 


26 


20 


14 



130,700 

75,800 

9 



MECHANICAL PROPERTIES WHEN HARDENED 



Tensile Strength (in pounds 
per square inch) 

Elastic Limit (in pounds per 
square inch) 

Elongation (percentage in 2 
inches) 



66,400 


73,100 


99,400 


132,100 


153,400 


40,300 


39,600 


54,000 


81,400 


102,100 


24 


22 


14 


9 


4 



180,100 

105,500 





EFFECT OF COMPOSITION AND HARDENING ON THE STRENGTH OF CARBON 

STEEL 

This is best shown by the above table , in which it will be seen that 
the tensile strength and elastic limit gradually increased with the increase 
in the percentage of carbon, both in the annealed and hardened state, 
while the elongation gradually decreased. These tests were made with a 
bar I inch in diameter and 4 inches in length. It will also be seen that 
there was considerable change in the steels that were too low in carbon to 
be made so hard that they could not be filed. The reduction in elonga- 
tion when the test bars were heated and quenched showed that the metal 
was harder than when in the annealed state. 

A hardening process that will produce a steel that is as homogeneous 



HARDENING STEEL 199 

as possible is always sought for in practice. This is easily obtained in 
a high-carbon steel, and especially if it contains 0.85% carbon, by passing 
the upper recalescent point before quenching. The desired homogeneity 
is not so easily obtained, however, in the low-carbon steels as they have 
several points of transformation. If these are quenched at a point a little 
above the lowest point of transformation, the carbon will pass into solu- 
tion, but the solution is not homogeneous. To obtain this result it is 
necessary that the quenching be done from a little above the highest 
pointlof transformation. This is higher in low- than high-carbon steels. 
In practice this calls for a quenching of the low-carbon steels at about 
1650° F., while a high-carbon steel should be quenched at about 1450°. 

The degrees of temperature, above the critical point, that the steel 
can be heated in practical commercial work and still give good results 
are also quite important. If a piece of steel be quenched from different 
tem.peratures above the point of transformation and examined under a 
microscope we find that the higher we go the coarser will be the marten- 
site, and the lines will be more visible. If we raise this temperature a 
few hundred degrees above the critical point and quench in a very cold 
bath, austenite makes its appearance. In regard to the mechanical 
properties the higher the temperature above the critical point the lower 
will be the tensile strength and the less will be the hardness of the steel. 
The elongation will also show a decrease and this will mean that the steel 
becomes more brittle with each increase in the temperature. 

This coarsening of the martensite, the reduction of both the tensile 
strength and elongation and the crj^stallization spoken of some few para- 
graphs back, have led to the conclusion that, in practice, 40° F. above 
the highest point of transformation is the extreme limit that steel should 
be raised to obtain the best results in hardening- The same figure also 
holds good for annealing. 

The following results are obtained in hardening steel: All steels may 
be hardened, but if the carbon content is over 0.30% the effect is more 
pronounced. Hardening increases the tensile strength and elastic limit 
and reduces the elongation, the effect being greater the greater the carbon 
content. Quenching at the proper temperature gives the metal a greater 
homogeneity and this aids the resistance to shock, especially in low- 
carbon steels; steel should not have the hardening temperature raised 
more than 40 degrees above the highest point of transformation, as 
beyond that it no longer has the same qualities. 

BATHS FOR HARDENING 

As it is necessary to maintain the metal in the state it was at the 
moment quenching begins, the quenching bath is a very important part 
of the process of hardening. The rate of cooling is never swift enough 



200 COMPOSITION AND HEAT-TREATMENT OF STEEL 

to secure perfection, and the intermolecular transformation will be more 
or less complete according to the rate of cooling. The better the bath 
the nearer to perfection we will be able to arrive. 

The baths for quenching are composed of a large variety of materials. 
Some of the more commonly used are as follows; they being arranged 
according to their intensity on 0.85% carbon steel: Mercury; water with 
sulphuric acid added; nitrate of potassium; sal ammoniac; common salt; 
carbonate of lime; carbonate of magnesia; pure water; water containing 
soap, sugar, dextrine, or alcohol; sweet milk; various oils; beef suet; 
tallow; wax. These baths, however, do not act under all conditions 
with the same relative intensity, as their conductivity and viscosity vary 
greatly with the temperature, and their curves of intensity are theiefore 
very irregular and cross each other frequently. Notwithstanding the 
many special compounds that have been exploited for hardening, there 
are no virtues, or hardening and toughening properties, in any quenching 
bath beyond the degree of rapidity with which it conducts the heat out 
of the piece being quenched. 

With the exception of the oils and some of the greases, the quenching 
effect increases as the temperature of the bath lowers. Thus water at 
60° will make steel harder than water at 160°. Sperm and linseed oils, 
however, at all temperatures between 32° and 250° F., act about the same 
as distilled water at 160°. The influence of the bath depends upon its 
nature, its temperature, and its volume; or, in other words, on its specific 
heat, conductivity, volatility, and viscosity. When the bath is in con- 
stant use, the first piece quenched will be harder than the tenth or twen- 
tieth, omng to the rise in temperature of the bath. Therefore, if uniform 
results are to be obtained in using a water bath, it must either be of a 
very large volume or kept cool by some mechanical means. In other 
words, the bath must be maintained at a constant temperature. 

In Fig. 120 is shown the effect of different hardening temperatures 
on the tensile strength and elongation when quenching in different baths. 
These tests were made at the Watertown arsenal. 

The mass of the bath can be made large, so that no great rise in tem- 
perature occurs by the continuous cooling of pieces, or it can be made 
small, and its rise in temperature used for hardening tools that are to 
remain fairly soft. If this temperature is properly regulated, the tool 
will not have to be reheated and tempered later, and cracks and fissures 
are not as liable to occur. A lead bath, heated to the proper temperature, 
is sometimes used for the first quenching. Another way of arriving at 
the same results would be to use the double bath for quenching, that is, 
to have one bath of some product similar to salt, which fuses at 575° F. 
Quench the piece in that until it has reached its temperature, after which 
it can be quenched in a cold bath or cooled in the air. 



HARDENING STEEL 



201 



The specific heat of the bath is an important factor, as the more rapid 
the coohng from 1650° to 200° F., the more effective will be the hardening 
process. These are the temperatures at which the transformation that 
corresponds to the hardening process begins and ends. A bath that 
consists of a liquid which volatilizes easily at the highest temperature 
it reaches, from plunging the metal into it, forms a space around the steel 
that is filled Avith vapor, and this retards the further cooling action of the 
liquid. The motion of the bath will throw off these vapors as it brings 
the liquid in contact with the metal and tends to equalize the temper- 
ature. The agitation of the piece to be hardened will give better results 



120,000 

110,000 

100,000 

J 90,000 
u 

I 80,000 
ra 

I 70,000 

CO 

3 60,000 

o 

a 

[g 50,000 

ID 
U 

M 40,000 

_o 

'S 

S 30,000 
H 

20,000 
10,000 



Chemical composition - Carbon .20, Manganese .58, Silicon .015, Phosporus .017. 



'1 
































■s 




iP 


jjss^ 


























^, 


—^^ 


r 


s.A^i> 




,w^ 




■ 






















-^ 






^0^ 
























§ / ■- 


'& 


y 

5^* 


t\»^ 


d. eC"^^ 


jii:- 
























\pp 








to ^'^' 


ealeJ »> 


cherry ._ 

































I/' 






^ 




JjlijilS 


p^ 






















X^ 


^ 


natura\_ 


jW^ 


























^ 


r1 


























/ 
































( 

































































12 3 4 5 6 

Elongation - percent . 



10 11 12 13 14 15 16 



Fig. 120. — Effect of heat and mechanical treatment on the tensile stress and elongation. 

than trusting to the volatility of the bath, as it is more energetic in dis- 
tributing the vapors. 

The viscosity of the bath has an influence on the phenomenon of 
convection, which is the principal m.eans of the exchange of heat; the 
higher the viscosity the less its hardening effect. 

The conductivity of the bath has its effect on the exchange of heat 
between the piece to be hardened and the bath; therefore the greater the 
conductivity the more quickly the metal cools. 

As a rule little account is taken of the specific heat of the bath, but 
it is an important factor. As soon as the heated metal is plunged into 



202 COMPOSITION AND HEAT-TREATMENT OF STEEL 

the bath, the liquid begins to heat. The number of calories necessary 
for raising the temperature of the liquid a certain number of degrees 
will be the greater the higher the specific heat. Thus the cooling of the 
metal will heat the bath less the higher the specific heat of the latter, and 
consequently a bath is the more active the higher its specific heat. The 
less rapidly the equilibrium is established between the hardening bath 
and the metal quenched in it, the more active will be the bath. 

The specific heat of mercury is much less than that of water, and the 
cooling of quenched steel is three times as rapid in water as in mercury. 
The hardening effect is therefore much lower than that of water, but 
surface cracks and fissures are not nearly as liable to occur. 

METHODS OP KEEPING BATHS COOL , 

The baths, for hardening, that give the best results are those in which 
some means are provided for keeping the liquid at an even temperature. 
Of course, where but few pieces are to be quenched, or a considerable 
time elapses between the quenching of pieces, the bath will retain an 
atmospheric temperature from its own natural radiation. Where a bath 
is in continuous use, for quenching a large number of pieces throughout 
the day, some means must be provided to keep the temperature of the 
bath at a low, even temperature. The hot pieces from the heating fur- 
nace will raise the temperature of the bath many degrees, and the last 
piece quenched will not be nearly as hard as the first. 

When plain water is used it is easy to keep the bath cool by providing 
it with a pipe connecting it to the supply main and an outlet into the 
drain, and thus have a steady flow through the bath. Where a large 
amount of work is done and the water is paid for at meter rates, as in 
cities, this might be more expensive than having a large tank at an eleva- 
tion above the bath and a pump to force the water into it, thus using the 
water over and over again. This flowing of the liquid would do away 
with the necessity of agitating the steel in the bath, as when it is of the 
ordinary stationary kind, owing to the flowing liquid carrying away 
the coating of vapor which forms around the piece and prevents its cooling 
rapidly. 

A hole in the center of the bottom with an outlet on top is not a very 
good arrangement, as the cool current, striking the bottom side of the 
piece, is liable to cause it to warp. If the cool liquid is taken in at the 
bottom it should be taken in through several openings. A good method 
is to have the inlet covered with a spherical piece of sheet metal launched 
full of small holes that would deliver the liquid in fine streams similar 
to that of a sprinkling can. This would send the cool liquid to all parts 
of the bath. 



HARDENING STEEL 



203 



A still better arrangement would be to have an extra inner wall with 
a large number of fine holes punched in the sides and solid at the bottom. 
This would cause the cool liquid to flow in from aU sides, which would 
give the bath a complete agitation and subject the pieces to less irregu- 
larity of temperature, and would therefore reduce the tendency of the 
pieces to spring or warp from not cooling equally on all sides. A variation 




Fig. 121. — Water spray quenching bath. 



of this is sho'wn in the spray bath in Fig. 121. In this A is a circular 
gas pipe, into which is screwed the perforated upright pipes C, C, and 
B is the intake pipe. The water comes through the fine holes in pipes 
C, C, and forms a spray on the lines D, D. 

With liquids, other than water, this method is not practical owing to 
the large volume of liquid needed for the bath, and its consequent high 
cost. Then again the losses from evaporation might be too great. For 



204 COMPOSITION AND HEAT-TREATMENT OF STEEL 

this kind of bath a water-jacketed .receptacle could be used and a steady 
current of cold water kept flowing through it, or the bath could be fitted 
with a coil of pipe, over the bottom and around the sides, through which 
a circulation of cold water- could be maintained, and thus keep the bath 
cool by radiation. Another , method that has been used successfully 
is to blow fine sprays of air through the bath from the bottom similar 
to the method used in the Bessemer converter on molten steel. One 
way of doing this is shown in Fig. 122. 

With many classes of work a bath whose liquid is stationary and has 
no mechanical means of cooling can be used by having the volume of 
the bath large enough to work off the heat left by the quenching of the 
pieces. Baths of this character are sometimes fitted with conveyors 
that carry the work through the bath, and out after cooling sufficiently. 
Some of these also carry the work through a pickling bath after it has 
been quenched. 



Fig. 122. — Pipes for cooling a quenching 
bath. 

ELECTRICAL HARDENING 

There is another method of hardening that is coming into use, and 
promises some interesting developments in the future. It consists of 
connecting the piece of steel to the positive and negative wires of an elec- 
trical circuit, and inserting it into a quenching bath. The current is 
then turned on and controlled l")y a rheostat, so that the metal can be 
heated to the proper temperature. This takes but a few seconds, and 
when the correct temperature is reached, the current is turned off and 
the steel is suddenly cooled or quenched in the bath in which it was 
heated, without being removed. In one case the bath was made of a 
solution of carbonate of potash and water. The piece is heated .so quickly 
that is does not raise the temperature of the bath to a degree that retards 
the hardening effects. 



HARDENING STEEL 205 

This process prevents the scaUng or bhstering of the steel, as it is 
not brought into contact with the air when hot, and hence oxidization 
cannot take place. It also is capable of many variations, as a piece can 
be locally heated and hardened in the bath, or annealed in spots by heating 
it outside of the bath. The piece can also be placed on a copper plate 
and an electric arc used to heat any desired portion of it. It can then 
be quenched to harden, or annealed, as desired. In dra^^^ng the temper 
on the inside of a hollow object, a rod can be inserted in the hole and 
this heated up until the desired color of the steel has been reached and the 
current then turned off. By noting the amount of current consumed on 
a few test pieces, it can be regulated, by means of the rheostat, so that 
uniform results can be obtained on any number of pieces. The possi- 
bilities that this method suggests may make it an important factor in 
the future in heat-treating steels. 

CEACKING AND WARPING 

Much serious trouble has been caused by cracks and fissures that have 
been produced by the abrupt cooling of steel. Many times a piece sep- 
arates abruptly from the part quenched. The reason for this is easily 
given, as during the cooling different parts of the steel are at different 
temperatures. This is many times caused by thick and thin sections in 
the same piece, but it also occurs in pieces of an even thickness, owing 
to the transformation in temperature not taking place everywhere at 
the same time. This causes internal strains, which many times attain 
enormous value and result in the lessening and also stopping of the cohesive 
force that holds the molecules of the metal together. This causes brittle- 
ness and rupture at the places so affected. 

In practical work the main thing to keep in mind is that these fissures 
only occur in high-carbon steel or some of the special alloys. There are 
several waj^s of overcoming this, and the three which are the easiest to 
use and most certain in their results are as follows: 

First. — When a water-quenching bath is used it may be covered 
with from \ to 1 inch of oil, which will reduce the rate of cooling. 

Second. — A quenching bath of comparatively small size may be used, 
in which case the sudden cooling will be followed by a slight tempering 
effect, caused by the rise in temperature of the bath. 

Third. — The piece may be withdrawn from the bath before it is com- 
pletely cooled. Uniform results are hard to obtain bj^ this last method, 
owing to the cUfhculty of judging the temperature at which the metal 
is when withdrawn. 

Warping maj^ be caused bj'' several factors, the two most important 
of which are, not having the steel in a proper condition of repose before 



206 COMPOSITION AND HEAT-TREATMENT OF STEEL 

it is hardened, and not putting the piece in the quenching bath properly. 
As any operation of working steel is liable to set up internal strains it 
is always best after rolling, forging, or machining steel to thoroughly 
anneal the piece before hardening it. This allows the metal to assume 
its natural state of repose. In the machining operations the roughing 
cuts could be taken off, the piece annealed, then the finishing cuts could 
be given it and the piece hardened. This would also make the steel 
easier to machine, as the metal is more uniform and in its softest state. 

There are several rules that can be followed in hardening a piece of 
steel to prevent warping, and these rules always assume that the piece 
has been properlj' annealed before starting the hardening operations. 

First. — A piece should never be thrown into the bath, as by l^iying 
on the bottom it would be liable to cool faster on one side than the other 
and thus cause warping. 

Second. — The piece should be agitated, so the bath will convey its 
acquired heat to the atmosphere, and also destroy the coating of vapor 
that is liable to form on certain portions, and thus prevent its cooling 
as rapidly here as in the balance of the piece. 

Third. — The liquid of the bath should instantaneously cover the 
largest possible amount of the surface of the piece when plunged into it. 

Fourth. — Hollow pieces, such as spindles, should have the ends plugged, 
as they could not otherwise be quenched vertically on account of the 
steam that would be produced in the hole and cause it to throw hot water. 

Fifth. — Pieces with thin and thick sections, or of intricate shapes, 
should be immersed so the most bulky parts would enter the bath first. 

Sixth. — To harden one part of a piece only, it should be immersed 
so that it hardens well beneath the heated part. 

Seventh. — Pieces which are very complicated should be rigged up 
with hoops, clamps, or supports to prevent their warping. 

The hardening of large pieces gives somewhat different results as the 
transformation is not alwaj's complete, in which case there is a partial 
return to the normal stable state, that is, toward pearlite. Thus a small 
piece quenched from a high temperature in cold water is very hard and 
quite brittle, while a large piece quenched at the same temperature and 
under the same conditions is not quite as hard and only slightly brittle. 
If the large piece is examined with the microscope it would indicate mar- 
tensite to be present in the surface layer, while at a certain distance below 
the surface would be seen troostite and sorbite. This would show that 
the transformation was not as complete as in the small piece and would 
account for the lower degree of hardness and brittleness. 

This might lead one to suspect that the constituents in the center of 
a large piece were the same as in annealed steel, as the coefficient of expan- 
sion and the electrical resistance seem to be the same. From this might 



HARDENING STEEL 



207 



be drawn the conclusion that the mechanical properties of the two steels 
were not the same. These, however, are not the facts as the strengths 
and hardness are but little different from those of the small piece that 
showed martensite. 

On all steels, it is a very good rule that insists on a slow preheating 
of the metal before it is submitted to the high temperature of the harden- 
ing heat furnace. If followed, this will prevent, to a large extent, the 
checking, cracking, warping, etc., that is met with so often in the harden- 
ing room. To get the best results, low-carbon steels should consume 




Fig. 123. — Tempering plate with sheet 
iron oven. 



about one hour in being heated up to a temperature of not less than 
600° F. ; high-carbon steels should be preheated to about 800°, and some of 
the special alloy steels, especially high-speed steel, to not less than 1000°. 
If even a higher temperature than this is reached in the slow heating, 
it will benefit rather than harm the metal, although at about these tem- 
peratures a transformation in the grain of the metals takes place that 
enables it to be heated more rapidly without any practical injury to the 
steel. 

The preheating need not be made a matter of much expense to a hard- 
ening room, as low heat tempering furnaces are nearly always available, 



208 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



or if not ovens could be placed over the high heat furnaces. One of the 
simplest arrangements for slowly preheating is the hot plate that is 
16 X 24 inches and covered with a sheet-iron oven, as shown in Fig. 123. 
It has 6 rows of 30 small gas jets underneath the plate, and any desired 
temperature can be attained in the oven. A small muffle furnace, similar 
to that shown in Fig. 124, is also very useful for preheating, and this can 
be used for reheating carbonized work. Both of these furnaces can be 
easily and successfully used for tempering, and thus the preheating not 
made an item of expense. 




Fig. 124. — Muffle gas furnace. 

The principles and practices of hardening are practically the same 
for the special alloyed steels as for the ordinary carbon steels, except 
that some of the alloying materials alter the point of transformation. 



HIGH-SPEED STEELS 

There is one notable exception to this, however, and that is in the 
case of high-speed or self-hardening steels. These are made by alloying 
with the steel, tungsten, and chromium, or molybdenum and chromium, 
or all three. These compositions completely revolutionize the points 
of transformation. Chromium, which has a tendency to raise the critical 
temperature, when added to a tungsten steel, in the proportions of 1 or 
2%, reduces the critical temperature to below that of the atmosphere. 
Tungsten and molybdenum prolong the critical range of temperatures 



HARDENING STEEL 



209 



of the steel on slow cooling so that it begins at about 1300° F. and spreads 
out all the way down to 600°. 

These steels are heated to from 1850° to 2450°, and cooled moderately 
fast, to give, them the property known as "red-hardness." Sometimes 
they are cooled in an air blast, and sometimes they are quenched in 
various liquids. This treatment prevents the critical changes alto- 




FiG. 125. — Cylindrical gas, hardening furnace. 



gether, and preserves the steel in the austenitic condition. The austen- 
itic condition is one of hardness and toughness, and it is peculiar that 
under this heat treatment the steel is not transformed into the pearlitic 
condition. 

One rule that has given good results in heat-treating some high-speed 
steels is to heat slowly to 1500° F., then heat fast to from 1850° to 2450°; 
after which cool rapidly in an air blast to 1550°; then cool either rapidly 
or slowly to the temperature of the air. 



210 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



HARDENING FURNACES 

The furnaces used for heating steel up to the necessary temperatures 
for hardening should be so arranged that the oxygen of the air will not 
attack the metal when it is hot, as then oxygen has its greatest affinity 
for iron, and will combine with it to form oxides that result in scale, blis- 
ters, etc. The flame must therefore be a reducing one, that is, consume 
all of the oxygen before it has a chance to attack the metal, or a retort 
for holding the work must be used, and this heated from the outside by 
flames that are not permitted to enter the retort. 




Fig. 126. — Cylindrical oil, hardening furnace. 



Many furnaces that are suitable for hardening steel are shown in 
Chapter VIII, but there are various other styles. On long slender work 
it is often necessary to heat them, in a liquid or otherwise, with the ends 
hanging down, and for that reason furnaces of the style shown in Figs. 
125 and 126 are the most suitable. These can be made to use either 
gas or oil for fuel. 

When it comes to the high temperatures that are needed for high- 
speed steel, specially designed furnaces are the most economical. The 



HARDENING STEEL 



211 



furnace shown in Fig. 127 is one of these, and the details of its construc- 
tion are shown in Fig. 128. A temperature of 2500° F. can be attained 
in 20 minutes, and maintained at that figure. The blast pressure gener- 
ally used is about 2 pounds per square inch. Though usually confined 
to small work, the furnace can be used for long articles, as an opening at 
the back allows for the introduction of long bars, or drills. Two hori- 
zontal burners, each conveying air and gas in concentric tubes, enter 
the furnace on opposite sides and at different levels. By an arrange- 
ment of channels in the lining of the furnace, the flame is given a rotary 




Fig. 127. — Wizard high-speed steel 
furnace. 



motion, with the result that the whole of the interior of the heating 
chamber is filled with flame, which passes round the circular walls of the 
chamber, at a high speed, and out through the flues at the back. Hence 
the products of combustion pass to the exhaust box, that is located 
under the actual furnace. Through this box pass the pipes conveying the 
incoming gas and air, so that a regenerative action is set up, and as soon 
as the furnace is in blast, both the gas and air are preheated. 

Another style of high-speed steel furnace is shown by the vertical 
type in Fig. 129. A movable fire-clay plate, which can be raised or low- 



212 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




Fig. 128. — Sectional view of wizard high-speed steel furnace. 





*- n 






i 




1 


9T' : i 



Fig. 129. — Vertical high-speed steel 
furnace. 



HARDENING STEEL 213 

ered by means of a rack and pinion, is used for inserting the work in the 
furnace. When raised, it forms the bottom of the furnace, by fitting into 
a circular cavity, and the hardener need not stand in the full glare of 
the opened furnace while he extracts the tool. It has the flame injected 
into the heating chamber at an angle so it will be given a rotating motion 
and thereby heat all parts of the chamber uniformly. As heat rises and 
cold descends the temperature of the furnace is not reduced as much 
when it is opened at the bottom to insert the tools as would be the case 
with a side or top-opened furnace. For this reason, also, the flame is 
inserted near the bottom of the furnace. The entire top is a cover that 
is made of fire-clay and held together by a steel band, with handles for 
lifting it off. In its center is a small peep-hole with a cover fitted in. 



CHAPTER XI 

Tempering Steel 
methods, materials used, and results obtained 

Negative quenching consists of cooling the metal through the critical 
zone at a rate equal to or below that which will give to the metal the 
greatest elongation when cold. This rate of cooling separates the mechan- 
ical results of quenching into the two distinct divisions mentioned farther 
back, namely, that for giving a cutting edge to tools, and that for increas- 
ing the static strengths and dynamic qualities. It varies as an inverse 
function of the carbon content unless the elements used in the special 
alloys influence it. 

Negative quenching gives a tensile strength and elastic limit about 
equal to that obtained in annealed steel, and produces the highest 
possible elongation and a high reduction of area. This usually gives the 
steel the highest obtainable resistance to shocks. 

As positive quenching becomes more and more pronounced it increases 
the tensile strength and elastic limit; at first slowly, then more and more 
rapidly, and reduces the elongation and resistance to shock in the same 
ratio. Thus, bj^ variations in the factors governing the activity of the 
quenching bath, any steel may be given its most suitable state for any 
given purpose. In fact, all possible methods of quenching are but means 
of varying the rate of cooling, and the selection of the cooling mediums 
which will give the desired rate of cooling through each of the critical 
temperature zones of the metal in order to give it the desired properties 
is the real art of heat treatment. 

Tempering steel, therefore, is to return it to a state of molecular equi- 
librium at atmospheric temperature by relieving any strains in the metal 
which have been caused by sudden quenching, and correct any exaggera- 
tion of certain properties which have been caused by the hardening 
process. 

The temperature to which a piece should be raised for tempering 
depends on the use to which it is to be put, the condition in which it has 
been left by quenching, and the composition of the metal. The maxi- 
mum temperature desired should only be maintained long enough to 
be sure that the piece is evenly heated. The austenite which is retained 

214 



TEMPERING STEEL 



215 



in steel by the sudden cooling has a natural impulse to change into pearlite. 
Steels which have been reheated slightly after hardening give a freedom 
to the molecular change that will lessen the molecular rigidity set up 
by the hardening process. The higher the temperature is carried in reheat- 
ing, the more it will lessen this molecular rigidity, and the more will the 
austenite give way to a pearlitic formation. 

Steels heated to 150° F. will be slightly tempered, but if heated to 
the temperature at which the straw color is formed on a brightened 
surface by the appearance of an iron oxide, namely 450°, a greater tem- 
pering will result, and the temperature at which this oxide assumes a 
permanent blue color, namely 575°, will effect a still greater tempering. 
Each increase in this temperature of reheating reduces the hardness and 
brittleness, reduces the tensile strength and elastic limit, and increases 
the elongation as well as the resistance to shocks. 

Steels that are not exposed to shock, and require a great hardness so 
that a fine cutting edge can be given them, such as razors, can have 
a marked degree of brittleness. A reheating to 450° F. for tempering will 
be the best condition that such steel can be given. Tools which have 
to withstand violent shocks such as cold-chisels and still retain a good 
cutting edge should be reheated to 575° to further remove some of the 
brittleness. This will lessen the hardness, and consequently the cutting 
powers, but is the lesser of the two evils. These two cases might be taken 
as the two extremes of temper desired in cutting tools. 

The temperature to which it is best to draw or temper tools is about 
as follows: 



430° F., or a Faint Straw Color: 
Tools for Metal Planers. 
Small Turning Tools. 
Hammer Faces. 
Steel-engraving Tools. 
Wood-engraving Tools. 



Ivory-cutting Tools. 
Bone-cutting Tools. 
Paper Cutters. 
Scrapers for Brass. 



460° F., or a Dark Straw: 
Punches and Dies. 
Screw-cutting Dies. 
Leather-cutting Dies. 
Wire-drawing Dies. 
Taps. 

Milling Cutters. 
Metal-boring Cutters. 
Reamers. 



Tools for Wood Planers. 
Inserted Saw Teeth. 
Knife Blades. 
Wood-molding Cutters. 
Tools for Cutting Stone. 
Rock Drills. 
Half-round Bits. 
Chasers. 



216 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



500° F., or a Dark Brown: 
Wood-boring Cutters. 
Edging Cutters. 
Hand-plane Cutters. 
Coopers' Tools. 

530° F., or a Light Purple: 
Hack Saws. 
Axes. 
Wood Bits and Augers. 

550° F., or a Dark Purple: 
Cold-chisels for Steel. 
Chisels for Wood. 
Circular Saws for Metal. 



Flat Drills. 
Twist Drills. 
Drifts. 
Wood Gouges. 



Dental Instruments. 
Surgical Instruments. 
Springs. 



Needles. 
Gimlets. 
Screw-drivers. 



570° F., or a Light Blue: 
Cold-chisels for Iron. 
Saws for Wood. 



Molding Cutters to be filed. 
Planer Cutters to be filed. 



The temperatures of the different colors used for tempering are about 
as follows: 



Faint Straw, 430° F. 
Straw, 460° F. 
Light Brown, 490° F. 
Dark Brown, 500° F. 
Purple and Brown, 510° 



F. 



Light Purple, 530° F. 
Dark Purple, 550° F. 
Light Blue, 570° F. 
Dark Blue, 600° F. 
Blue Green, 630° F. 



These colors of steel, at a given temperature, cannot always be depended 
upon, however, as the various ingredients that enter into the composition 
of different grades of metal are liable to influence the color. That the 
carbon contents of steel has an influence on the colors is shown by the 
samples in Fig. 130. These pieces were carbonized and hardened, then 
tempered at various temperatures, as measured by a pyrometer, and it 
is to be regretted that the colors cannot be shown, although the contrast 
between the low-carbon center and the high-carbon outer shell can be 
seen. Some of these pieces were left rough, as they were broken and 
others were ground and polished before hardening. 

The pieces A and B are I X If inches, and A is untreated, while B 
was hardened and then drawn until the high-carbon outer shell was a 
greenish-blue color. The difference between the two colors showed a 
decided contrast; C and D were ground and polished and then hardened 



TEMPERING STEEL 



217 



and drawn until the outer shell was a dark blue. This left the low-carbon 
center a dark brown. These pieces were | inch diameter; E was hard- 
ened and not drawn. This left the shell a bright steel color, while the 
center was almost a black; F was drawn to a dark blue, and this left the 
center a dark brown, similar to the pieces C and D; piece G was drawn 
to a purple, and this left the center a yellow brown or dark straw color; 
the H piece was drawn to a dark brown in the shell, which left the center a 
light straw color; L was drawn to a full purple, which left the center a 
spotted red brown; M was drawn to a full blue in the shell, and this left 
the center a brown purple; J was drawn to a dark blue, which left the 
center a dark brown, while piece K was hardened and drawn to a purplish 
blue, and this left the center a light brown. Pieces /, N, P, and were 
drawn to a dark blue on the high-carbon outer shell, and this left the 
low-carbon center a dark brown. 




Fig. 130. — Carbonized steel after being hardened and drawn to color. 



While the hardening of steel by colors has been successfully done 
in the past, and will be done many times in the future, these -pieces would 
seem to make it imperative for the hardener to test a sample piece from 
each lot of steel before attempting to harden it by color. A much better 
way, however, would be to use a pyrometer for measuring the temper- 
atures as, if the pyrometer is kept in order, a positive knowledge of the 
temperature at which the metal is treated can be instantly obtained, 
and the differences in the light in the shop or even in color-blindness will 
not affect the hardener. 

Steels that are used in the building of machinery, as a rule, have the 
temper drawn much more than this, and the variation in temper is only 
limited by the work that the parts have to do, the composition of the 
metal, and the different degrees of temper which steel can be given. Leaf 
springs, such as carriage springs, are usually reheated to about 800° F. 



218 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



Gears which are in constant mesh without any undue pressure will 
give the best results as to wear, strengths, and resistance to shocks 
if reheated to about 675°. Crank-shafts on internal-combustion engines 









































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have to withstand considerable torsion, vibrational strains, and im- 
pact stresses and seem to stand the work best when reheated to 
about 1000°. 

Fig. 131 and 132 show the effect of the above heat treatment for 



TEMPERING STEEL 



219 



springs on two kinds of steel which might be said to show the two extremes 
in deflection, fiber stress, and their resultant permanent set. In Fig. 
131 the elastic limit was reached on the second test. This for the vana- 
dium steels was 85,000 pounds, or 234,500 pounds fiber stress with a per- 
manent set of 0.48 inch. In the carbon steels it was 65,000, or 180,000 
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took an additional set of 0.26 inch on the third test and broke on the 
fourth in the center. The third test was repeated three times on the 
vanadium steel without any change in recorded hights. The tests were 
made by the American Vanadium Company. 

The rate of cooling after reheating to the proper degree for tempering 
is immaterial, as when we reheat a piece, say to 400°, we have changed 
the constituents of the metal all that we can without increasing this tem- 



220 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



perature. Thus a piece might be held at this 400° for an hour and the 
change would be no more than that made in the first few seconds, as no 
change will take place during the cooling. 

The changes that can be made in the strengths of steel are very 
forcibly shown in the following Table No. 2, which explains itself: 

Table No. 2 





Tensile Strength 


Elastic Limit 


Elongation in 


Reduction of 




Lb. per Sq. In. 


Lb. per Sq. In. 


2 In., Per Cent. 


Area, Per Cent 


Annealed at 1475 degrees 


87,640 


64,400 


29 


59 




125,000 


103,000 


21 


56 




127,800 


110,100 


20 


58 


Hardened at 1650 degrees, oil 


130,500 


124,000 


17 


62 


tempered at varying quench- 


138,000 


127,500 


18 


65 


ing temperatures 


147,000 


140,750 


17 


57 




212,000 


200,000 


12 


51 




232,750 


224,000 


11 


39 



TEMPERING EQUIPMENT 



The furnaces used are sometimes the same as those used in hardening. 
But furnaces that will permit of maintaining a constant temperature 
with appliances for measuring the heat so the correct temperature can 
be attained are the best kind. Thus, wherever possible it is best to have 
furnaces that are designed especially for tempering. These can be built 
cheaper than hardening and annealing furnaces, as it is not necessary 
to construct them so they will withstand the high heats used in hardening, 
and special appliances can be attached that are not needed on the harden- 
ening or annealing furnaces. 

The oven gas furnace shown in Fig. 133 is a very handy one in which 
to temper work, and oil fuel can be used on this style of furnace if desired. 
The hot plate with a sheet metal oven, that is shown in Fig. 123, is also 
very useful for tempering. Another type of the gas furnace for temper- 
ing is shown in Fig. 134. This is very useful for small work which is 
inserted through the opening *S into the drum D, and the door E closed. 
The drum is then rotated by a gear and worm on shaft N, and the work 
tumbled so all the pieces will be uniform in temper and heated on all 
sides. Drum D can be pulled out of the furnace by handle H, to empty 
out the work when it is finished. The heat can be accurately controlled 
at the desired temperature by gas valve G, and air valve A, and reference 
to the thermometer T. 



TEMPERING STEEL 



221 



Lead baths are used a great deal, as it is easy to heat these to a certain 
temperature and hold them at a constant temperature for any length 
of time. With this the bath is heated to the temperature at which the 
steel needs to be tempered or drawn, the piece is placed in the bath and 
allowed to remain until it has attained the temperature of the bath, and 
it is then taken out and cooled. One of the simpler gas-heated lead baths 
is shown in Fig. 135. These, however, can be heated with coal, coke, 




Fig. 133. — Oven furnace with gas for fuel. 



oil, or any other fuel as well, and they should be supplied with a hood 
that is piped to the outside, as any fumes that may arise from the molten 
lead are injurious. 

As the pure lead melts at about 620° F., it is necessary to mix it with 
some other metal to get the lower tempering temperatures. Tin is the 
most often used for this purpose, as it lowers the melting temperature 
sufficiently, and is a comparatively cheap metal. As low as 300° for the 
melting point can be obtained by combining these two metals. The 
alloys that will melt at given temperatures are as follows: 



222 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




Fig. 134. — Revolving drum tempering furnace. 



TEMPERING STEEL 223 

Pure Lead melts at 619° F. 

200 parts Lead and 8 parts Tin melt at 560° F. 

100 parts Lead and 8 parts Tin melt at 550° F. 

75 parts Lead and 8 parts Tin melt at 540° F. 

60 parts Lead and 8 parts Tin melt at 530° F. 

48 parts Lead and 8 parts Tin melt at 520° F. 

39 parts Lead and 8 parts Tin melt at 510° F. 

33 parts Lead and 8 parts Tin melt at 500° F. 

28 parts Lead and 8 parts Tin melt at 490° F. 

24 parts Lead and 8 parts Tin melt at 480° F. 

21 parts Lead and 8 parts Tin melt at 470° F. 

19 parts Lead and 8 parts Tin melt at 460° F. 

17 parts Lead and 8 parts Tin melt at 450° F. 

16 parts Lead and 8 parts Tin melt at 440° F. 

15 parts Lead and 8 parts Tin melt at 430° F. 

14 parts Lead and 8 parts Tin melt at 420° F. 




Fig. 135. — Gas-heated lead bath. 



Oil baths are also used quite extensively for tempering, and like the 
others the bath should be maintained at the temperatures to which it 
is desired to draw the temper, and the work immersed until it has attained 
the temperature of the bath and then taken out to cool in the air. One 
of the best oil bath furnaces is that shown in Fig. 136, but equally good 



224 COMPOSITION AND HEAT-TREATMENT OF STEEL 

results are obtained with oil-fired or electrically heated baths. The tem- 
perature can be easily controlled by means of the gas and air valves, 
as in the other furnaces shown, by using the high temperature thermom- 
eter for a guide. The wire basket shown in front of the furnace is to 
hold the work so it can be easily removed from the oil. 

Temperatures of 600° F. can be easily obtained and maintained 
in the oil baths with the ordinary oils, but for temperatures that are much 
higher than this other materials should be used. Some of the tallows 




Fig. 136. — Gas-heated oil bath. 

can be successfully worked at temperatures as high as 800°. Steel is 
not injured by soaking in the oil for an indefinite time, provided the 
desired temperature for tempering has not been exceeded. This makes 
it possible to temper large and small pieces at the same time, as while 
the large pieces are lying in the bath to thoroughly absorb the heat in 
all their parts, the smaller pieces can be tempered. It is always best to 
slowly preheat the work to from 300° to 400° before submitting it to the 
tempering bath, as this allows the molecules of the metal to readjust 
themselves more thoroughly than if the piece is plunged immediately 
into the tempering bath. 

The electrically heated oil bath is doubtless the best, as by means 



TEMPERING STEEL 



225 



of the rheostat the temperature is very easily controlled. When the 
exact amount of current that is required to heat a given oil up to a given 
temperature is known, the rheostat can be set at this and no further 
attention paid to it until the work is ready to be taken out of the bath. 
When starting with a cold bath no preheating of the work is required 
as the rheostat can be set and the work heated up with the oil. To main- 
tain a temperature of 600° F. in one style of electrical oil bath, it required 




Fig. 137. — Tempering furnace with revolving retort. 



6 kilowatts per hour for 9 gallons of oil, 7.2 kilowatts for 11 gallons, and 
20 kilowatts for 20 gallons. 

Salt baths are sometimes used where the drawing temperature desired 
is 575° F. Salt fuses at this point, and a certainty of obtaining this tem- 
perature in the steel is assured. In using this the salt is heated to 700° 
or 750°, and the steel placed in the bath. When this is done the cold 
metal will cause the salt which surrounds it to solidify and plainly show 
a, white crust around it. When the steel has attained a temperature 



226 COMPOSITION AND HEAT-TREATMENT OF STEEL 

of 575° the white crust will disappear as the salt which made it has melted 
and mixed with the rest of the bath. This clearly shows that it is time 
to take the piece out of the bath and allow it to cool. This method can 
be used for tempering above 575° and below 900°, but is not practical 
for higher or lower temperatures owing to the alteration in the salt of 
which it is composed. 

Another method that is used considerably on some classes of work 
is sand tempering. This consists of covering the work with sand, and 
heating both up at the same time. Clean and well-dried sand is some- 
times used in a pan, and the metal heated up in it over a fire. Some 
special gas furnaces have also been built for sand tempering in which the 
sand is permanently kept at the required temperature. The work is 
placed in this until it has thoroughly attained the temperature of the 
sand, and then cooled in the air. Continuous operating automatic gas 
furnaces have also been made for sand tempering. In these the work 
and sand travels through the furnace, from one end to the other, by the 
aid of a worm. The work is then dumped out, while the sand is brought 
back to the other end, inside of the furnace, by means of a second worm. 

A gas furnace, with a revolving retort, that is used for tempering is 
shown in Fig. 137. The outer shell of the furnace is lined with fire- 
brick, and this is heated by the gas. The round retort, the opening of 
which is shown at the end, is placed inside of the outer shell, and revolves 
on 4 wheels, two of which are at each end of the furnace. It is revolved 
by means of bevel gears, sprockets and chains, and a pulley and belt. 
The whole is mounted on trunnions, and can be tilted to any angle so 
the work will travel through the furnace automatically. This furnace 
is also used to give metal parts a gun-metal finish. This color can only 
be given to pieces that will stand tempering to 600° F., as it takes that 
temperature to put the color on the metal; this being done by means of 
charred bone and chemicals. 



CHAPTER XII 
Carbonizing 

methods and materials used — effect of alloying materials and 

heat treatment 

Many of the steels that give very high figures in their strength 
tests are made hard enough to resist wear for such parts of machinery 
as gears, cams, ball races, etc., by hardening and tempering; but when 
the proper degree of hardness is obtained to reduce wear to a minimum, 
they are too brittle to withstand shock strains. 

For this reason case-hardening, carbonizing, or, as it is called in Europe, 
"cementation," is resorted to, as by this process the outer shell can be 
made hard enough to resist wear, and the core of the piece can be left 
soft enough to withstand the shock strains to which it is subjected. By 
this method gears can be made from some of the special alloy steels that 
will reduce the wear to a point that would have been considered impos- 
sible a few years ago, and at the same time resist shock to such an extent 
that it is very difficult to break out a tooth with a sledge hammer. 

Several methods different from the old established one of packing 
the metal in a box filled with some carbonizing material, and then sub- 
jecting it to heat, have been devised in the last few years. Among them 
might be mentioned the Harveyizing process which is especially appli- 
cable to armor plate. This in turn has been followed by an electrical 
and a gas process, which claim to be great improvements over the Har- 
veyizing process. Very recently another process has been invented which 
uses gas for carbonizing in a specially constructed furnace. This is very 
useful for carbonizing small work. 

The Harveyizing process uses a bed of charcoal over the work, and 
a bed of clay over that. The plates are pressed up against it in a pit 
or furnace, and gas turned on so that the steel will be heated through 
the charcoal, thus allowing the carbon to soak in from the top. 

This process has been a great success, but it also has its faults, as the 
carbon soaks in to a good depth in some places, while at other places, 
sometimes only a foot away, the carbon will not be so deep, so that when 
tested a shot will glance off from one spot, and when it hits a short dis- 

227 



228 COMPOSITION AND HEAT-TREATMENT OF STEEL 

tance from this will tear a great hole in the plate. Then again the 
Harveyizing process has not been adaptable for small work. 

Electricity has also been used in a like manner to the gas in the 
Harveyizing process. That is, armor plate has been covered with a layer 
of ground bone, the whole enclosed and a current of electricity turned 
on to heat the bone and metal so that the carbon will combine with the 
steel in a surface layer of varying depths, and it is claimed for this process 
that the depth can be regulated to any depth desired, and the carbon 
is of an even depth over the entire surface. 

As these two processes are only used on armor plate or other large 
work of a similar character, and are at most too expensive in their instal- 
lation to be made applicable to parts of machinery, or tools, they will 
not be gone into in detail here. 

The Krupp process is similar to the above two in the kind of work 
it operates on, and differs from Harveyizing in that it uses a gaseous hydro- 
carbon to replace the bed of charcoal. This also is foreign to the subject, 
but the gas it uses is practically the same as that used in the furnace for 
carbonizing with gas, which will be described later. 



FACTOES GOVERNING CARBONIZING 

The result of the carbonizing operation is determined by five factors, 
which are as follows: First, the nature of the steel; second, the nature of 
the carbonizing material; third, the temperature of the carbonizing fur- 
nace; fourth, the time the piece is submitted to the carbonizing process; 
fifth, the heat treatment which follows carbonizing. 

The nature of the steel has no influence on the speed of penetration 
of the carbon, but has an influence on the final result of the operation. 
If steel is used that has a carbon content up to 0.56%, the rate of pene- 
tration in carbonizing is constant; but the higher the- carbon content, 
in the core, the more brittle it becomes by prolonged annealing after 
carbonizing. Therefore it is necessary that the carbon content should 
be low in the core, and for this reason a preference is given to steels con- 
taining from 0.12 to 0.15% of carbon for carbonizing or case-hardening 
purposes. Some, however, prefer a steel containing from 0.20 to 0.22% 
carbon, owing to its being more easily worked with machine tools; but 
the results will not be as good as with a steel containing a maximum of 
0.15% carbon. Greater strength and easier working qualities can be 
obtained by the addition of such alloys as chromium, vanadium, titanium, 
nickel, etc. 

Manganese. — It is also very important that the manganese content 
of carbonizing steels be kept low. This should never exceed 0.35%, 



CARBONIZING 229 

as manganese has a tendency to render the hardened and carbonized 
surface brittle, thus making it hable to chip and break at the least shock. 
Thus manganese is usually kept down to 0.20%, and seldom exceeds 
0.25%. 

Chromium. — While chromium has a tendency to produce a mineral 
hardness in steel, it prevents the development of the crystalline struc- 
ture under heat treatment, thus refining the grain and making it better 
able to withstand shocks. Therefore chromium added in small per- 
centages makes steels for carbonizing more homogeneous, and imparts 
to them greater strengths and wearing qualities. Chromium, however, 
produces steels that are very difficult to machine; it is therefore com- 
bined with other ingredients which offset this, except for such uses as 
armor plate. 

Vanadium, used in homeopathic doses, overcomes this difficulty of 
machining chrome steels to such an extent that it is claimed that a 
steel containing 1% chromium and from 0.16 to 0.18% vanadium, can 
be forged and machined as easily as a 0.40% carbon steel. Vanadium 
also produces high dynamic strengths, which gives the core of carbonized 
steels a high resistance to shocks. 

Titanium produces practically the same results as vanadium in steels 
for carbonizing, and is usually used in percentages of from 0.40 to 0.50. 

Nickel, added to ordinary carbonizing steel in comparatively small 
percentages, obviates the brittleness which is usually produced by car- 
bonizing, and makes it more homogeneous, the pearlite being distributed 
much better. With 2% of nickel, the steel is increased in strength; 
in some cases this strength is nearly double that of the ordinary carbon- 
izing steel, but 2% nickel steel means nothing unless the carbon is of 
the proper percentages. When it is, it makes one of the best of steels, 
when carbonized and tempered, for such parts as shafts, ball races, gears, 
etc. It should therefore be used wherever the 2| cents difference in price 
does not make it prohibitive, except where the higher priced alloy steels 
are demanded, owing to their greater strength and wearing qualities. 

A 2% nickel steel carbonized so that the surface layer contains about 
1% of carbon will be pearlitic, but a 7% nickel steel will show a surface 
layer that is martensitic, with a pearhtic core. Martensite being a con- 
stituent of quenched steel, a 7% nickel steel carbonized so the surface 
layer contains 1% of carbon, has the same constitution as an ordinary 
carbonizing steel that has been carbonized and hardened, that is, a pearl- 
itic core and a martensitic outer shell. This martensite should become 
denser and denser as it approaches the outer surface. If this 7% nickel 
steel is carbonized to a greater depth, so that the surface layer will con- 
tain 1.5% of carbon, the core will be pearlitic and resist shock to a great 
degree. A martensite layer will be next to the core and close to the outer 



230 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



layer. This will give high strengths, and the outer layer will readily 
polish without wear, thus giving it valuable wearing qualities. 

This simplifies the processes of carbonizing, owing to its doing away 
with the hardening processes afterward, but the carbonizing and the 
cooling afterward must be carefully done in order to get good results 
from this process. If, however, the proper carbonizing materials are 
used, the heat of the furnace regulated so that it remains steady and at 
the proper temperature, and the piece not cooled too quickly, a saving 
in time and expense can be made with this process of carbonizing, when 
this grade of steel is suitable. 

The influence of the different elements on the speed of penetration 
of the carbon, when carbonizing steels containing the same amount of 
carbon and different percentages of manganese, chromium, nickel, tung- 
sten, silicon, titanium, molybdenum, and aluminum, is shown by Table 3. 

Table 3. — Penetration of Carbon Per Hour 



Component of Alloys 



Speed of Pene- 
tration Per 
Hr. in Inches 



Component of Alloys 



Speed of Pene- 
tration Per 
Hr. in Inches 



0.5 per 
1.0 per 
1.0 per 
2.0 per 
2.0 per 
5.0 per 
0.5 per 
1.0 per 
2.0 per 
0.5 per 



cent, 
cent, 
cent, 
cent, 
cent, 
cent, 
cent, 
cent, 
cent, 
cent. 



manganese, 
manganese, 
chromium . 
chromium . 

nickel 

nickel 

tungsten. . . 
tungsten. . . 
tungsten. . . 
silicon 



0.043 
0.047 
0.039 
0.043 
0.028 
0.020 
0.035 
0.036 
0.047 
0.024 



1.0 per 
2.0 per 
5.0 per 
1.0 per 
2.0 per 
1.0 per 
2.0 per 
1.0 per 
3.0 per 



cent, 
cent, 
cent. 
cent, 
cent, 
cent, 
cent, 
cent, 
cent. 



siUcon 

silicon 

silicon 

titanium .... 
titanium .... 
molybdenum 
molybdenum 
aluminum. . . 
aluminum. . . 



0.020 
0.016 
0.000 
0.032 
0.028 
0.036 
0.043 
0.016 
0.008 



The rate of penetration for ordinary carbonizing steel under the same 
conditions would have been 0.035 inch. Thus it will be seen that man- 
ganese, chromium, tungsten, and molybdenum increase the rate of pene- 
tration. These seem to exist in the state of a double carbide and release 
a part of the cementite iron. 

Nickel, silicon, titanium, and aluminum retard the rate of penetra- 
tion — 5% of silicon reducing it to zero — and these exist in the state 
of solution in the iron. The titanium steel, however, has more titanium 
in it than should be present in carbonizing steel, and if this were reduced 
to 0.50% an increase would probably be shown instead of a retardation. 
As it is, the 1% of titanium only very slightly retarded the penetration. 

As a general rule the alloyed steels that give the best results in anneal- 
ing, hardening, and tempering are not the best for carbonizing; for this 



CARBONIZING 231 

reason most of these alloyed steels are made in a special grade for car- 
bonizing. As an illustration of this, vanadium steel that gives the best 
results for crank-shafts, transmission shafts, connecting rods, and other 
moving engine parts is composed of 0.25 to 0.30% carbon, 0.40 to 0.50% 
manganese, 1% chromium, and 0.16 to 0.18% vanadium, while the best 
carbonizing steel has from 0.12 to 0.15% carbon, 0.20% manganese, 
0.30% chromium, and 0.12% vanadium. 



CARBONIZING MATERIALS 

The nature of the carbonizing materials has an influence on the speed 
of penetration, and it is very essential that the materials be of a known 
chemical composition, as this is the only way to obtain like results on 
the same steel at all times. 

These materials or cements are manufactured in many special and 
patented preparations. The following materials are used and compounded 
in these preparations, but many of them give as good results when used 
alone as when compounded with others in varying percentages: Powdered 
bone, wood charcoal, charred sugar, charred leather, cyanide of potas- 
sium, ferrocyanide of potassium, black oxide of manganese, bichromate 
of potassium, animal black acid cleaned, prussiate of potash, anthracite, 
mixture of barium carbonate, graphite, petroleum gas, acetylene, ammonia, 
naphtha, carbon monoxide, horn, etc. Some have used illuminating gas 
and gasohne, but these act by dissociation and are not definite or positive 
enough for good results. 

Such materials as bone and leather should not be used alone or in 
combination, as it is impossible to obtain definite results from them, 
owing to the changeability of their chemical composition when subjected 
to a temperature high enough for carbonizing. 

Wood charcoal is very largely used in carbonizing steels, but the 
value of this material varies with the wood used, the method employed 
in making the charcoal, and other factors. Used alone it gives the normal 
rate of penetration for the first hour, but after that the rate gradually 
decreases until at eight hours it gives the lowest rate of penetration of 
any of the carbonizing materials. 

The best wood charcoal is that made from hickory. This is due to 
the fact that wood charcoal contains a percentage of carbonate of potas- 
sium, and this, in conjunction with the charcoal and the nitrogen of the 
air, in the carbonizing case, is capable of giving cyanide of potassium. 
Thus, by combining wood charcoal and carbonate of potassium, an increase 
in the rate of penetration can be obtained; but this speed decreases with 
time, and the exhaustion of the cement is due to the volatilization of the 
alkaline cyanides. If a current of ammonia is used, the rate of penetra- 



232 COMPOSITION AND HEAT-TREATMENT OF STEEL 

tion becomes constant, as cyanide of ammonium is formed. Therefore 
some consider the best carbonizing materials to be the ones that produce 
the most of this element. 

Powdered charcoal and bone give good results as a carbonizing material 
and are successfully used in carbonizing nickel-chrome steel, by packing 
it in a cast-iron pot and keeping this at a temperature of about 2000° F. 
for four hours, and then cooling slowly before taking the metal out of the 
pot or removing the cover. 

Pure carbon, such as that of sugar, does not carbonize in vacuum; 
therefore a carbonizing material that is simply composed of carbon cannot 
act directly, but acts simply by dissolution of the carbon, starting with 
the iron in contact with it. Thus sugar should be mixed with some other 
material that will overcome this, in order to obtain the best results from 
carbonization. Carbonic oxide, giving 2C0 = C + CO2, which is formed 
by the action of the air, in the carbonizing box, on a carbonizing material 
that is composed simply of carbon, may act; but its action is slow, and 
the carbonic acid, CO2, has a decarbonizing action. This is the action 
which sugar, animal black (acid cleaned), etc., have. 

Materials containing a cyanide act by means of the cyanogen radical 
(CN)^. This compound is decomposed and replaces the carbon; it is 
in this manner that cyanide of potassium acts. The product is capable 
of producing cyanide, which is the case with a large number of cements. 
Ferro-cyanide of potassium gives cyanide, cyanate of potassium, and 
oxide of iron. The mixture of ferro-cyanide and bichromate of potash 
gives rise to a new mixture of cyanogen and cyanate diluted in a mass 
of iron and chromium oxide. This mixture and carbonate of barium are 
subjected to the same conditions. In fact, the mixture, in the presence 
of the nitrogen of the air, gives rise to cyanide of barium according to 
the following equation: 2N + 4C + COsBa = (CN)2Ba + SCO. There- 
fore it acts by means of cyanide and carbonic oxide. 

Certain carbonizing materials contain carbonates that are not dis- 
sociable at the temperature of carbonization, especially calcium carbonate. 
In the presence of carbon there is formed carbonic oxide, which carbonizes 
very slowly. 

Therefore the carbonizing materials might be classed as follows: First, 
cements which act by means of carbonic oxide; second, cements which 
act by means of a cyanide, such as potassium, barium, or ammonium; 
third, cements which act by means of hydrocarbons. To carbonize with 
the hydrocarbons, it is necessary to generate the gases in a tank and 
conduct this to the receptacle in which the work has been placed in such 
a manner that it will soak into the pieces before passing out of the vent. 

J. C. Oslon and J. S. Weissenback, at the Polytechnic Institute in 
Brooklyn, made some tests on carbonizing, with gases. They used f 



CARBONIZING 



233 



inch soft Norwegian iron that contained 0.08% of carbon, and the results 
are best shown in Table 4. 



Table 4. — Result of Experiment of Carbonizing Steel with Gases 



Test 
Number 



9 
10 
11 
12 
13 



Gas Used 



Illuminating and ammonia (a) . . . . 
Illuminating and ammonia (b) . . . . 
Illuminating and ammonia (c) . . . . 

Illuminating 

Illuminating and ammonia (a) . . . . 
Illuminating and ammonia (&).... 
Illuminating and ammonia (c) . . . . 
Carbon monoxide and ammonia (c) 

Carbon monoxide 

Acetylene and ammonia (c) 

Acetjdene 

Methane and ammonia (c) 

Methane 



Time 

in 
Hours 



Hard- 
ness 



glass 
glass 
glass 
none 
glass 
glass 
glass 
glass 
glass 
glass 
little 
little 
little 



Depth 

of Case, 

Inches 



0.004 

0.008 

0.008 

none 

0.012 

0.012 

0.012 

0.016 

0.016 

0.012 
not well defined 
not well defined 
not well defined 



Carbon 
Content, 
Per Cent. 



0.57 
0.66 

0.91 

none 

1.12 

1.16 

1.15 

1.45 

1.36 

0.98 

0.41 

0.32 

0.26 



The ammonia was used in different strengths a being the weakest 
with h twice the strength of a and c twice the strength of b. 

From the results shown in this table the conclusions were drawn 
that ammonia gas facilitates the case-hardening in all cases except that 
of carbon monoxide, which seems to act almost as well without as with 
ammonia. Of the three pure gases studied, the carbonizing abiUty is 
in the following order: Carbon monoxide, acetylene, methane. The 
illuminating gas not being a pure gas and varying in composition with 
the different gas companies, it cannot be given a fair comparison with 
the other gases. With illuminating gas and the strongest ammonia the 
4-hour test showed a very good percentage of carbon, and in the 8-hour 
test the percentages of carbon ran about equal in all of the three different 
strengths of ammonia. 

The results obtained from carbon monoxide show it to be by far the 
best gas for this purpose, and the difference in the carbon percentage 
between carbon monoxide alone and carbon monoxide combined with 
the strongest ammonia was so slight that it does not seem necessary to 
use ammonia with it. In the case of carbon monoxide the gas was 
freed from carbon dioxide by bubbling through strong caustic potash 
solution before entering the case-hardening tube. Roughly speaking, 
the hardening depth is for the four hours proportional to the time. 

Nitrogen. — The commonly used carbonizing materials all contain 



234 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



nitrogen in some form or other, and as the non-nitrogenous materials 
cost from one tenth to one-twentieth of those containing nitrogen, some 
experiments have been made with anthracite and coke. After carbonizing 
the same sized test pieces with these for four hours at 1650° F., the pene- 
tration for the anthracite was 0.006 inch, and with the best grade of hard 
coke it was 0.0064 inch. Charred leather under the same conditions gave 
a penetration of 0.062 inch. As this was in the proportions of 10 to 1 
it would lead to the conclusion that nitrogen performs an important 
part in carbonizing. 

The effect of ammonia was also tried by carbonizing in a gas pipe, 
and packing the work in sugar charcoal as the non-nitrogenous material. 
Dry ammonia was passed into one end of the gas pipe, and allowed to 
flow out through a small vent hole in the other end. The results obtained 
by carbonizing for four hours at 1650° were 0.058 inch for the charred 
sugar alone, and 0.070 inch for the charred sugar which had ammonia 
passing through it. The non-ammonia specimen was bluish-black in 
color, and when sawed appeared soft, while the ammonia-treated specimen 
was of a distinct whitish luster, and appeared to have a tough outer skin 
when sawed. 

Thus while all the evidence goes to prove that nitrogen aids carbon- 
izing in practical work, its action is not yet quite clear. Ammonia, on 
the other hand, is absorbed by the iron and becomes the prime agent 
in any change, thus causing an increase in the rate of carbonization. 

The speed of penetration caused by the action of different cements 
at different temperatures for the same time, i.e., eight hours, is best shown 
by Table 5. 

Table 5 





Materials Used ajsjd Rate of Penetration in 


Inches 


Degrees 
Fahrenheit 


Charcoal 60 per 

cent. + 40 per cent. 

of Carbonate of 

Barium 


. Ferro-eyanide 66 

per cent. + 34 per 

cent, of 

Bichromate 


Ferro-cyanide 
Alone 


Powdered Wood 
Charcoal Alone 


1300 










1475 


0.020 


0.033 


0.020 


0.020 


1650 


0.088 


0.069 


0.079 


0.048 


1825 


0.128 


0.128 


0.128 


0.098 


2000 


0.177 


0.177 


0.198 


0.138 



The nature of the carbonizing materials has a very pronounced effect 
on the rate of carbonization, or the percentage of the carbon content 
in the surface layer of the piece, or both. 



CARBONIZING 



235 



At the same temperature, i.e., 1825° F., for different lengths of time 
and with different cements, the rate of penetration obtained was according 
to Table 6. 







Table 


6 






Length of 

Time in 

Hours 


Materials Used and Rate of Penetration in Inches 


Carbon 60 per 

cent. + 40 per 
cent, of Carbonate 


Ferro-cyanide 66 

per cent. + 34 

per cent, of 

Bichromate 


Powdered 
Wood 

Charcoal 
Alone 


Charcoal and 

Carbonate of 

Potassium 


Unwashed 
Animal 
Black 


1 

2 
4 
6 
8 


0.031 
0.039 
0.047 
0.078 
0.118 


0.033 

0.037 
0.049 
0.074 
0.128 


0.028 
0.053 
0.063 
0.072 
0.098 


0.059 
0.078 
0.094 
0.011 
0.138 


0.035 
0.059 
0.088 
0.106 
0.128 



Eighty per cent, charcoal + 20% carbonate of barium, 40% charcoal 
+ 60% carbonate of barium, ferro-cyanide alone and 66% ferro-cyanide 
+ 34% bichromate were used with practically the same results for eight 
hours' time. 

Another set of tests was carried out for a longer period of time, with 
other materials and at a uniform temperature of 1650° F., with the results 
given in Table 7. 

Table 7 



Length of Time in 


Materials Used and Rate of Penetration in Inches 


Hours 


Charred 
Leather 


Ground Wood 
Charcoal 


Barium Carbonate and 
Wood Charcoal 


2 

4 

8 

12 


0.045 
0.062 
0.080 
0.110 


0.028 
0.042 
0.062 
0.070 


0.055 
0.087 
0.111 
0.125 



The test bars in this table were 3 inches long and | of an inch square. 
The chemical composition of the steel was as follows: Carbon, 0.14%; 
manganese, 0.58%; siHcon, 0.01%; sulphur, 0.08%, and phosphorus, 
0.03%. 

These tables show that charcoal when used alone gives the slowest 
rate of penetration, but when combined with other materials the rate 
of penetration is the highest of any of the tests made. In some cases 
the rate of penetration of the combined materials nearly doubles that 
of the wood charcoal alone. 



236 COMPOSITION AND HEAT-TREATMENT OF STEEL 

EFFECT OF TEMPERATURE 

The degree of carburization of the skin depends largely on the degree 
of temperature maintained during the carbonizing process; therefore it 
is necessary that the temperature be kept at a definite point in the car- 
bonizing of steels. This can best be done by attaching to the furnace 
something to gage the heat, such as a pyrometer. If the temperature 
is too high, the metal is liable to crystallize and the core will rapidly 
become brittle. And if too low the rate of penetration will be low. The 
temperature to which the metal can be safely raised in carbonizing varies 
with the kind of steel used. As a general rule the ordinary carbonizing 
steel cannot be raised to a temperature in excess of 1800° F. If the original 
carbon content is high, even this temperature cannot be safely reached, 
while with some of the alloy steels, such, for instance, as nickel-chrome 
steel, a carbonizing temperature of 2000° can be retained for four hours 
without the core crystallizing, and the rate of penetration will be reason- 
ably high, providing, of course, that the original carbon content is low. 

The temperature, however, must be kept above 1300° F., as ordinarily 
carbonization cannot take place below that point, although in an experi- 
mental way steel has been carbonized at about 850° by using a mixture 
of cyanide of potassium, chlorides of the alkalies, and the alkaline earths, 
the latter being used to lower the fusion point of the cyanide. 

The percentage of carbon which is absorbed by the steel is also affected 
by the temperature as well as by the materials used. With a given depth 
of penetration and a given amount of carbon in the carbonizing material, 
steel will absorb a greater percentage of carbon at a high temperature 
than at a low one. 

HEAT TREATMENT AFTER CARBONIZING 

The heat treatment following carbonizing should be very carefully 
done owing to the fact that the piece must have a very hard outer sur- 
face to resist wear, and a non-brittle core that will resist strains; also, 
some methods of heat-treating have a decarbonizing effect, and some of 
the steels have a tendency to produce cracks or fissures and to warp. 
Thus crank-shafts for internal-combustion engines were formerly car- 
bonized and hardened, but owing to the difficulty of preventing cracks and 
warping this practice has been abandoned. 

As a general rule the piece should be annealed after carburizing. This 
can best be done by leaving it packed in the carbonizing case, with the 
cover fastened on, and allowing it to cool gradually; but if the carbonizing 
temperature is not over 1600° F., it can be allowed to cool to 750°, then 
reheated to 1400°, and quenched with good results. If the carbonizing 
temperature is a high one, i.e., above 1800°, the piece should be allowed 



CARBONIZING 237 

to cool, then reheated to 1650°, and quenched and reheated again to 
1400° and quenched. 

The reason for the double quenching is that the piece must be heated 
to above its point of transformation, i.e., 1650°, to destroy the crystal- 
lization and consequent brittleness, which is liable to be in the core when 
it is carbonized at a high temperature; but this leaves the carbonated 
surface layer not hard enough to resist wear, therefore it must be quenched 
again at 1400°. This point of transformation varies with the different 
components of the high-grade alloy steels, and this should be ascertained 
before hardening the piece. • 

By quenching directly from the carbonizing retort a distinct line 
is formed between the high-carbon outer shell and the low-carbon cone, 
and this is liable to cause the metal to crack on this line when the work 
is used for parts similar to rollers in roller bearings, owing to the wearing 
and crushing strains to which they are submitted, but if the work is prop- 
erly heat-treated after carbonizing, this distinct line is made to disappear, 
and the danger of the steels cracking there is removed. 

Aside from the above rules, the general rules should be followed that 
are laid down for annealing, hardening, and tempering, in their respective 
chapters. 

TIME OF EXPOSURE 

The time that the work is submitted to carbonizing is an important 
factor, as the regulation of this under a given constant temperature is 
what gives the depth of carbon desired, and by the proper depth of the 
carbon is obtained the percentage of carbon desired in the surface layer. 
The percentage of carbon in a carbonized piece of steel gradually reduces 
from the outer shell to the core. The lower the carbonizing temperature, 
the less the time of submission to the carbonizing temperature, and the 
smaller the percentage of carbon in the carbonizing material the greater 
will be this reduction. 

A round bar of steel that was carbonized to the depth of fV of an 
inch was examined by turning off tV of an inch, and analyzing the turn- 
ings for carbon, then another sixteenth was turned off and analyzed, and 
the third and fourth sixteenth treated in a like manner. This gave a 
carbon content of 1.24% for the tV of an inch taken from the outside, the 
second sixteenth gave 0.85% carbon, the third sixteenth showed 0.24% 
carbon, and the fourth or core contained 0.13%. 

The time of submission required for a certain depth varies with the 
kind of carbonizing materials as well as with the process used. The 
carbonizing materials, such as powdered bone, charcoal, etc., which require 
that the work be packed in an iron box or pther receptacle, take con- 
siderable more time to carbonize the work than when gases are used to 



238 COMPOSITION AND HEAT-TREATMENT OF STEEL 

furnish the carbon, owing to the necessity of the heat penetrating the 
box and carbonizing materials before it can affect the work. In case a 
deep penetration of the carbon is required, and the carbon in the car- 
bonizing materials is nearly or entirely absorbed, it is a difficult opera- 
tion to insert fresh materials in the packing box. 

Another point might be mentioned here, and that is that all steels 
do not retain their carbonization. One specimen was examined by taking 
a very thin cut from the outer surface for a part of its length, which on 
analysis showed 1.25% of carbon. The piece was then laid aside for 
six months, and a similar cut taken from the rest of its length, which on 
analyzing showed only 0.92% of carbon. This showed that the carbon 
dissolved little by little into the mass. 



CAKBONIZING WITH GAS 

In the use of hydrocarbons, or gases, a fresh supply can be kept flow- 
ing into the carbonizing receptacle, and the time greatly reduced for 
deep penetration with an appreciable reduction of time for the shallow 
penetrations. 

A very important factor in carbonizing with gas is the furnace, as 
on the design and operation of this to a large extent depends the success 
or failure of the process. They are designed specially for this purpose, 
and are, therefore, not practical for use as hardening, annealing, or tem- 
pering furnaces, although they might be made useful for annealing or 
hardening large quantities of work by being fitted with appliances for 
handling the same. 

This makes the cost of installation higher than for the appliances used 
for carbonizing in the old way. The cost of carbonizing, however, is 
about one-half of that of the old method, which makes the furnace soon 
pay for itself by the saving in materials and labor. Where the cost of 
carbonizing is reduced to this extent it makes it commercially practical 
to carbonize steel parts that were considered prohibitive by the high 
cost and non-uniform results of the old method. Owing to the nature 
of the process of carbonizing by the old methods it is very difficult to 
obtain uniform results with pieces packed in the same box, or to repeat 
these results in other boxes. 

In order to judge the temperature of the pieces packed in a box it 
is necessary to insert test wires through the cover. After a certain time 
a test wire near the outer edge of the box is withdrawn and the temper- 
ature is found to be just right for carbonizing, but if one is drawn out of 
the center of the box at the same time it will be seen that the temperature 
here has not risen high enough, as it takes a much longer time for the 



CARBONIZING 239 

pieces in the center of the box to be raised to the proper temperature 
than for those near the outer surfaces of the box. 

As the carbonizing material must be packed in the box with the pieces, 
this means that the pieces near the sides of the box will begin to absorb 
the carbon before those in the center, and, therefore, the penetration 
will be greater. As the percentage of carbon in the outer surface of the 
pieces being carbonized is greater the greater the depth of penetration, 
it also means that the pieces near the outside of the box will have a greater 
carbon content on their surface than the pieces in the center, and this 
also means that they will be harder. 

Carbonizing with gas overcomes this to a large extent, if not entirely, 
as the carbonizing gas is not turned on until all of the pieces in the retort 
of the furnace have arrived at the proper carbonizing temperature, and 
it is shut off the minute the proper depth of carbonization has been ob- 
tained. The furnace can also be so regulated that the same results can 
be obtained with the next lot of pieces put in the retort. The carbon 
in the retort is also held constant by the steady flow of the gas, and the 
work can be inspected for temperature by shutting off the carbonizing 
gas and looking through the outlet pipe, where the work can be seen and 
its color noted. 

The special furnace for the gas carbonizing process is built and patented 
by the American Gas Furnace Company, and is shown in Figs. 138 and 
139. In Fig. 139, A is the retort in which the work is placed. This is 
made out of extra heavy 8-inch pipe, for the size of furnace shown, and 
is made to revolve on the rollers B, by the gear wheel C, and the worm D, 
which in turn is propelled by the sprocket wheel shown in Fig. 138. E E 
are air compartments to prevent the heat and work from getting into 
that part of the retort which extends beyond the heating furnace; F 
is the heating-gas chamber, the gas coming in through 5 openings or 
burners similar to the one shown at G, and exhausting out through others; 
H is the cover for the end of the retort, and is fastened on with hinged 
bolts and thumb screws. This is taken off in order to put the work in 
the retort, the partition / and carbonizing gas outlet J coming with it. 

The heating gas is fed through pipes and burners on the side, and the 
carbonizing gas passes through the hose sho^^^l above the sprocket wheel 
in Fig. 138, and then into that part of the retort where the work is held. 
After the carbon has penetrated the metal the gas escapes through the 
outlet J. 

In this process the carbonizing gas was vaporized from the liquids, 
naphtha and ammonia, and as the work is made to revolve in the furnace, 
similar to the action obtained by a tumbling barrel, an even depth of 
carbon is obtained on all sides of the work, and this overcomes, to a large 
extent, the tendency of carbonized pieces to have hard and soft spots. 



240 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



as the soft spots are usually caused by the piece coming in contact with 
something that would not allow the carbon to act on that spot. 

Pyrometers can be attached to the furnace to gage the heat for the 
correct temperatures, and when this has been attained the valves and 







IH^^BRI ^iviit^^wm^^^^^^"^ m 


^^^■H 


1 




1 



Fig. 138. — Revolving retort furnace for carbonizing with gas. 



cocks can be set so that the work can be duplicated for any number of 
times and the furnace run for a long period with an assurance of the quality 
of the work turned out, as the temperature is held constant. Starting 
with a cold furnace in the morning, an hour and a half is usually required 
to get the work hot enough to absorb the carbon. 

Odd-shaped and intricate pieces can be carbonized by this method 



CARBONIZING 



241 




242 



COMPOSITION AND HEAT-TREATMENT OF STEEL 




o 

J2 



3 
o 

5 



2 






CARBONIZING 



243 



that it would be difficult to do by packing in an iron box in such materials 
as bone and charcoal. This is best illustrated by the piece shown in Fig. 
140 that has been broken open to show the action of the carbonizing gas 
on the seven small holes around its rim, and it will be seen by a glance 
at the half-tone that the carbon penetrated to a good depth all around 
these holes. The piece to the left shows the surface that was broken 
at a distance of about 4 inches from the end to the right. It also showed 
that the carbon had a good even penetration as to depth on all of its 
exposed surfaces both inside and outside. 

The results of different lengths of time that the work is submitted to 
carbonization in this gas furnace is shown in Figs. 140 and 141. The 
distinct line between the carbonized shell and the core is obtained by 
plunging the metal directly from the carbonizing furnace into a quench- 
ing bath. By Fig. 141 is shown the depth of carbon that is obtained in 




Fig. 141. — Quenched directly from the carbonizing furnace. 

this furnace by carbonizing for 4, 8, 10, 12, 14, and 16 hours, and then 
quenching in a lard-oil bath directly from the furnace. The test bars 
were f inch in diameter, and are reproduced here at about their actual 
size. The results as to depths for this set of pieces is as follows: 



Time for Carbonizing in Hours 


Depth of Penetration in Inches 


4 


0.040 


8 


0.062 


10 


0.071 


12 


0.079 


14 


0.085 


16 


0.090 



The set of test pieces in Fig. 142 shows the depth of penetration for 



244 



COMPOSITION AND HEAT-TREATMENT OF STEEL 



3 
O 



o 






CARBONIZING 



245 



each hour, from 1 to 9 inclusive, as follows, as well as the size and shape 
of the piece: 



Time, Hours 


Size of Test Piece 


Depth in Inches 


1 


t in. round 


.015 


2 


i in. round 


.020 


3 


i in. round 


.030 


4 


8 in. round 


.038 


5 


i in. round 


.046 


6 


i in. round 


.053 


7 


i in. round 


.056 


8 


i in. round 


.058 


9 


i in. round 


.060 


9 


5 in. round 


.063 


9 


1 in. square 


.075 




-V32 Ead.- 



FiG. 143. — Samples of local hardening by carbonizing. 

Intricate or peculiar-shaped pieces that would not turn over in the 
furnace, but slide around on the bottom, would have very little carbon 
on the side that remained in contact with the retort. For these it would 
be necessary to put something inside of the furnace so constructed that 
it would cause them to turn over. Delicate pieces that would be liable 
to break would also have to have some special apparatus inside of the 
retort to protect them. 



246 COMPOSITION AND HEAT-TREATMENT OF STEEL 

LOCAL HARDENING 

The carbonizing process is often used for hardening certain parts of 
a piece, and leaving the rest soft, as illustrated by the pieces shown in 
Fig. 143. The three pieces are turned from machinery steel to the lines 
shown by the outside line of each piece. After this they are carbonized 
to the proper depth, then annealed, and then the parts shown by the 
sectional lines are turned off, after which they are hardened. 

By turning off the parts shown by the sectional lines, the outside layer 
that has been carbonized is turned off, and this leaves these parts with 
the machinery steel exposed. When hardening, therefore, the machinery 
steel does not harden, and consequently remains soft, while the balance 
of the pieces, which have a carbonized outer shell, do harden, and this 
makes the pieces hard in the parts desired and soft in the other places. 



INDEX 



Acetylene, 147, 231, 233. 
Acid Bessemer process, 17. 

hydrofluoric, 193, 195. 

open-hearth process, 27, 29. 

picric, 193, 197. 

sulphuric, 200. 
Alkali, chlorides, 236. 
AlkaUne cyanides, 231. 
Alkaline earths, 236. 
Alpha iron, 68. 

Aluminum, 75, 76, 83, 86, 88, 107, 109, 
118, 123, 144, 230. 

granular, 86. 
Ammonia, 231, 232, 233, 234. 

nitrate of, 195. 
Animal black, 231, 232, 234. 
Annealing, 185-191. 

cast-iron box for, 188. 

furnaces, 190. 

Howe's laws, 188, 189. 

laws of, 186. 

materials, 190. 

rules for, 187. 

temperature effects, 189. 
Anthracite, 231, 233. 
Antimonides, 89. 
Antimony, 78, 88, 89, 90, 175. 
Apatite, 79. 

Area, reduction of, 187, 214, 220. 
Arsenic, 42, 78, 88, 89, 90. 
Arsenides, 89. 

Austenite, 66, 195, 199, 209, 214- 
215. 

Barium, 232. 

carbonate, 231, 234. 

chloride, 175. 
Basic open-hearth process, 27, 30. 
Baths, barium chloride, 175. 

hardening, 199, 204. 

lead, 221-223. 

oil, 223-225. 

salt, 225-226. 

tempering, 221-226. 



Bessemer process, 1, 6, 13. 

Beta iron, 68. 

Bichromate of potash, 232, 234, 235. 

of potassium, 231. 
Billets, 19. 

Bismuth, 78, 88, 89, 90. 
Blast furnace, 1-12. 

combined electric and, 10-12. 
Blooms, 19. 
Blow-holes, 14, 30, 31, 72, 75, 76, 83, 106, 

107, 108, 117, 120. 
Bone, 228, 231, 232, 237. 
Borate of hme, 91. 
Borax, 93. 
Boric acid, 91. 
Boron, 91. 
Braunite, 71. 
Briquettes, ore, 12. 
Brittleness, 237. 

Calcium, 75. 
Campbell process, 32. 
Carbide of iron, 74, 193. 
Carbon, 9, 10, 12, 13, 22, 29, 33, 34, 39, 
45, 50, 64, 65, 66, 67, 69, 70, 71, 74, 
76, 79, 80, 82, 86, 87, 88, 116, 118, 
119, 123, 124, 126, 144, 152, 193, 195, 
198, 199, 201, 216, 227, 229, 230, 231, 
232, 236, 237, 238. 
combined, 1, 4, 193. 
content, 68. 
dissolved, 193. 
graphitic, 1, 4. 
speed of penetration of, 228. 
Carbonate, 71. 

of barium, 231, 234. 
of Hme, 200. 
of magnesia, 200. 
Carbonic oxide, 75, 232. 
Carbonizing, 227-246. 

depth of, penetration in, 230, 233, 

234, 235, 243-245. 
effects of elements in, 230. 
electrical, 228. 



247 



248 



INDEX 



Carbonizing, factors governing, 228-231. 

furnace, 239. 

gas process of, 238-245. 

Harveyizing process, 227. 

heat treatment after, 236. 

Krupp process, 228. 

local, 246. 

materials, 231-235. 

rates of penetration in, 234, 235, 243- 
245. 

temperature effect on, 236. 

time of exposure, 237. 
Carbon monoxide, 13, 83, 231, 233. 
Case-hardening (see Carbonizing), 227-246. 
Casting, 116. 
Castings, 1. 

direct-steel, 121. 

gray iron, 6. 

steel, 27. 

steel, properties of, 118. 

Tropenas process, 117. 
Cast iron, 18. 
Cementation process, 65. 
Cementite, 66, 79, 193, 194, 195, 196, 197. 
Cerium, 110. 
Charcoal, 9, 12, 31, 65, 190, 227, 231, 232, 

234, 235, 237. 
Charred bone, 190. 

leather, 190. 

sugar, 231, 232, 234. 
Chloride of barium, 175. 

of alkali, 236. 
Chrome-nickel, 100. 

-vanadium, 100. 
Chromium, 36, 50, 60, 69, 74, 93, 99, 102, 
122, 123, 124, 208, 228, 229, 230, 231. 

oxide, 232. 
Cobalt, 97, 98. 
Cohesive force, 205. 
Coke, 1, 4, 12, 17, 31, 233. 
Compression, limit of, 186. 
Conductivity, 200, 201. 
Converter, Bessemer, 13, 14, 17. 
Copper, 42, 75, 86, 87, 88. 
Copper sulphide, 87. 
Corrosion, 28, 85, 88. 
Cracking, 205-208, 236. 
Critical temperatures, 193, 199. See also 
Recalescent, Decalescent, and Trans- 
formation points. 
Crucible process, 1, 6, 34. 



Crucibles, fire-clay, 34. 

graphite, 34. 
Crystalline structure, 114. 
Crystalhzation, 237. 

of anneahng, 187. 
Cupola, Spiegel, 15. 
Cupro-titanium, 108. 
Cyanate, 232. 

of potassium, 232. 
Cyanide, 178, 236. 

alkahne, 231. 

ferro-, 231, 232, 

of ammonia, 232. 

of potassium, 175, 231, 232, 236. 
Cyanogen, 232. 

Decalescent points, 68. 
Decarbonization, 27. 
Deflection, 218, 219. 
Dolomite, 17. 
burned, 30. 
Dynamics, 197. 
Dynamic properties, 229. 

Elastic limit, 189, 192, 198, 199, 201, 214, 

215, 218-219, 220. 
Electric blast furnace, 8-12. 
Electric current for iron furnaces, 11. 
Electric furnaces, see Furnaces, electric. 
Electric process, 1, 6. 

welding, 145-147. 
Electrical conductivity, 193. 
Electrodes, 9, 11, 12. 
Elongation, 189, 198, 199, 201, 214, 215, 

220. 
Erosion, 195. 
Eutectic steel, 67. 
Ferrite, 66, 87, 92, 116, 193, 194, 195, 196, 

197. 

Ferro-aluminum silicon, 60. 
-boron, 91. 
-chromium, 99. 
-cyanide, 36. 

-cyanide of potash, 232, 234, 235. 
-manganese, 29, 31, 36, 71, 84, 85, 107, 

108. 
-mangano-aluminum-silicon, 60. 
-mangano-silicon, 61. 
-silicon, 29, 75, 76, 77, 78, 86, 108. 
-silicon-manganese, 71, 75. 



INDEX 



249 



Ferro-titanium, 18, 19, 105, 107, 120. 

vanadium, 120. 
Ferrous-titanate, 105. 
Fiber stress, 219. 
Fire-clay, 190. 
Fluorspar, 86. 
Fluxes, 45. 
Flux, magnetic, 50. 
Forging, 122-124. 

drop-hammer, 131-135. 

hand, 126. 

press, 136-143. 

steam-hammer, 127. 

temperatures, 124-125. 
Fuels, furnace, 153-181. 

crude oil, 155. 

gaseous, 163. 

hard, 153. 

kerosene, 154. 

liquid, 154. 

producer gas, 163. 
Furnace, electric, Colby, 49. 

Girod, 56. 

Heroult, 45. 

Keller, 47. 

Kjellin, 49. 

refining, 40. 

Stassano, 42. 

Richling-Rodenhauser, 53. 

Combined gas and electric, 63. 
Furnaces, blast, 1-12. 

carbonizing, 239-245. 

combined electric and blast, 10-12. 

electric, 42-57. 

electric smelting, 8-12. 

hardening, 210-213. 

heat treatment, 151-184. 

barium-chloride bath, 178. 

cyanide of potassium bath, 175. 

electric, 182-184. 

gaseous fuel, 163-181. 

temperature regulator for, 170. 

hard fuel, 153. 

lead bath, 175. 

liquid fuel, 154-163. 

liquid heating, 174-181. 



Gases, occluded, 18, 19, 30, 77, 83, 104 
Gasoline, 231. 
Graphite, 66, 194, 231. 

Hammer, hardness, 187. 

hard steel, 186. 

steel, 38. 
Hardening, 192-213. 

baths, 199-204. 

carbon effects in, 198. 

cracking in, 205. 

effects of, 199. 

electrical, 204. 

factors in, 193. 

furnaces, 210-213. 

high-speed steels, 208. 

mechanical effects of, 198. 

preheating in, 207. 

temperatures, effects of, 200. 

warping in, 206. 
Hardenite, 195-197. 
Hardness, 192, 215, 227. 
Harvey izing, 65. 
Hematite, 62. 
Horn, 231. 

Hot-blast stoves, 1-4. 
Hydrocarbon, 83, 232, 236. 
Hydrofluoric acid, 193, 195. 
Hydrogen, 66, 83, 84, 85, 149. 

Illuminating gas, 231, 233. 

Impact, 218. 

Ingots, 16. 

Internal strains, 185, 205, 214. 

Iodine, tincture of, 193, 197. 

Iridium, 94. 

Iron, blast-furnace, 16. 

carbide, 193. 

cast, 18. 

ore, 1, 4. 

oxide of, 28, 29, 215, 232. 

phosphide of, 73. 

pig, 1, 9, 10, 12, 13, 30. 

wrought, 30, 36, 37, 40. 

Krupp process, 66. 



Gamma iron, 68. 

Gases, carbonizing, 228, 231, 232, 233, 
234, 238-245. 
illuminating, 231, 233. 



Ladle cars, hot metal, 5. 
Lanthanum, 110. 
Lash mixture, 61. 
process, 61. 



250 



INDEX 



Lead bath, 221. 

-tin baths, 221-223. 
Leather, charred, 231, 234. 
Lime, carbonate of, 200. 

slacked, 190. 
Limestone, 1, 4, 17, 25, 28, 30, 86. 

burnt, 56. 

Machinery steel, 68. 
Magnesia, 17, 190. 

carbonate of, 200. 
Magnesite, 30, 47. 
Magnesium, 150. 

oxides, 79. 
Magnetic, 193. 

qualities, 192. 
Magnetite, 61. 

Manganese, 1, 13, 14, 15, 29, 31, 32, 36, 
38, 39, 40, 50, 63, 65, 69, 71, 72, 73, 
74, 75, 76, 77, 80, 83, 85, 86, 88, 101, 
102, 116, 118, 119, 121, 122, 123, 
124, 126, 198, 201, 228, 230, 231. 
Manganese, ferro-, 29, 36, 71, 73. 

oxide, 29, 30, 73, 231. 

silicate, 82. 

sulphide, 14, 19, 73, 81, 85. 
Manganite, 71. 
Martensite, 110, 195, 196, 197, 198, 199, 

206, 207, 229. 
Martin process, 22. 
Mercury, 200, 202. 
Methane, 233. 
Mica, 190. 

Microscopical examination, 193-197. 
Mill, slabbing, 19, 111. 

tilting table, 111. 
Molds, ingot, 16. 
Molybdenum, 102, 103, 208, 230. 
Monell process, 32. 
Monel metal, 95. 

Naphtha, 231. 

Nickel, 34, 42, 50, 60, 74, 93, 95, 96, 97, 
99, 120, 123, 144, 228, 229, 230. 
chrome, 42, 236. 
Nitrate of ammonia, 195. 

of potassium, 200. 
Nitrogen, 83, 84, 104, 105, 106, 107, 117, 

118, 231, 233-34. 
Non-magnetic, 185, 193. 



Oil baths, 223-225. 
Open-hearth process, 1, 13, 22. 

acid, 1, 6. 

basic, 1, 6. 
Ore, 17. 

briquettes, 12. 
Overheating, 152. 
Oxidation, 28. 
Oxide, 210. 

carbonic, 232. 

chromium, 232. 

magnesium, 79. 

manganese, 198. 

of iron, 28, 215, 232. 

scale, 210. 
Oxidizing, 188. 
Oxy-acetylene, 147. 

Oxygen, 1, 13, 19, 29, 30, 40, 45, 73, 76, 
83, 84, 85, 86, 117, 118, 119, 147, 
176, 190, 210. 
Oxy-hydrogen, 149. 

Pearlite, 66, 87, 92, 110, 194, 195, 215, 229. 

of, 228. 
Petroleum gas, 231. 
Permanent set, 218-219. 
Phosphate of lime, 79. 
Phosphide of iron, 73. 
Phosphides, 78, 89. 

Phosphorus, 1, 13, 17, 18, 19, 28, 29, 30, 
31, 32, 38, 40, 42, 46, 47, 56, 63, 65, 
74, 77, 78, 79, 80, 81, 85, 88, 117, 
118, 124, 126, 198, 201. 
Picric acid, 193, 197. 
Pig-casting machines, 7, 8, 9. 

iron, 9, 10, 12. 
Pigs, 1, 4, 6, 8. 
Platinum, 94. 
Potash, bichromate of, 232, 234, 235. 

ferro-cyanide of, 232, 234, 235. 

prussiate of, 231. 
Potassium, 36, 75. 

cyanate, 232. 

cyanide, 231, 232, 236. 

ferro-cyanide, 231, 232. 

nitrate, 200. 
Prussiate of potash, 231. 
Pyrometers, 164. 

Quenching baths, 199-204. 



Occluded gases, 18, 19, 30, 77, 83, 104. 



Rails, steel, 17. 



INDEX 



251 



Rails, steel, sulphur in, 19. 
Recalescent points, 67, 185, 192, 193, 199. 
See also Critical and Transformation 
points. 
Recarburized, 22. 
Recarburizing, 15, 31. 
"Red-hardness," 209. 
Reduction of area, 187, 214, 220. 
Refractory earth, 190. 
Rolling, 111-114. 

rules for, 115. 

temperatures, 116. 
Rolls, slabbing. 111. 

Sal ammoniac, 200. 
Salt, 36, 200. 

baths, 225-226. 
Sand annealing, 190. 

siUca, 6. 

tempering, 226. 
Sawdust, 190. 
Scaling, 188. 
Scrap, steel, 28. 
Shock resistance, 192, 199, 215, 218, 227, 

229. 
Silica, 29, 30, 74. 
Silicates of iron, 75. 
Silicide, 75. 
Silicious materials, 29. 
SiUcon, 1, 14, 16, 17, 29, 30, 31, 34, 37, 38, 
39, 40, 63, 65, 71, 75, 76, 77, 78, 80, 
83, 85, 86, 94, 116, 118, 119, 123, 124, 
126, 198, 201, 230. 

dioxide, 75. 

-ferro, 29, 75, 76, 77, 78. 

ferro-manganese, 71. 

in electric furnace, 77. 

in iron, 12, 13 . 

oxidation of, 29. 

results on quenching, 76. 

Spiegel, 76. 
Slag, 10, 16, 19, 25, 27, 29, 30, 40, 56, 76, 119. 

lime-iron-oxide, 60. 

oxidizing, 79. 
Slig, 12. 
Sodium, 75. 

Sorbite, 189, 195, 197, 206. 
Sows, 4, 6, 8. 

Specific heat, 200, 201, 202. 
Spiegeleisen, 15. 
Spontaneous annealing, 187. . 



Static strength, 197, 214. 

Stove, hot-blast, 1-4. 

Strains, internal, 185, 205, 214. 
vibrational, 218. 

Stress, fiber, 219. 

Sugar, charred, 231, 232, 234. 

Sulphide of iron, 81. 
of manganese, 81. 

Sulphur, 1, 13, 18, 19, 28, 29, 30, 31, 32, 
38, 40, 42, 46, 47, 56, 63, 65, 73, 74, 
80, 81, 82, 83, 84, 85, 86, 117, 118, 119, 
124, 126, 190, 198. 

Sulphur in coke, 12. 

in electric-furnace iron, 12. 

Sulphuric acid, 200. 

Talbot process, 22. 
Tantalum, 93. 
Tempering, 186, 214r-226. 

colors, 216. 

crank-shafts, 218. 

effects of, 220. 

furnaces, 220-226. 

gears, 218. 

sand process, 226. 

springs, 217. 

temperatures, 215-216. 
Tempering furnaces, gas, 220. 

electrically heated, 224. 

lead bath, 221. 

oil, 220, 223. 

salt bath, 225. 
Tensile strength, 29, 186, 187, 189, 192, 

198, 199, 201, 214, 215, 220. 
Tincture of iodine, 193, 197. 
Titaniferous ores, 105. 
Titanium, 18, 19, 84, 86, 105, 108, 120, 

123, 228, 229, 230. 
Titanium-, cupro-, 108. 
Titanium, ferro-, 18, 19, 120. 
Tool steel, 68. 
Torsion, 218. 

Transformation point, 185, 186, 187, 188, 
189, 190, 192, 193, 197, 199, 208-209 
214, 237. See also Recalescent, De- 
calescent, and Critical Points. 
Troostite, 197, 206. 
Tropenas process of casting, 117. 
Tungstates, 101. 

Tungsten, 34, 42, 50, 60, 69, 100, 101, 102, 
123, 124, 208, 230. 



252 



INDEX 



Tuyeres, 4, 12. 

Uranium, 103. 

Vanadium, 84, 86, 99, 103, 104, 105, 119, 
120, 123, 144, 228, 229, 230, 231. 

chrome, 34, 105. 

ferro-, 120. 
Vibrational strains, 218. 
Viscosity, 200, 201. 



Volatility, 200, 201. 

Warping, 205-208, 236. 
Welding, 143-145. 

electric, 145-147. 

oxy-acetylene, 147. 

Thermit, 149-150. 

with gases, 147-149. 
Wolframite, 101. 



OCT. 7 Ml 



One copy del. to Cat. Div. 



m 



ISC 



